Exhibit 99.1

Byline Bancorp, Inc. Reports Second Quarter 2017 Financial Results

Second Quarter 2017 Summary

Chicago, IL, July 27, 2017 – Byline Bancorp, Inc. (NYSE: BY), the holding company of Byline Bank, today reported net income of $6.1 million for the second quarter of 2017, compared with net income of $6.6 million for the first quarter of 2017, and net income of $2.6 million for the second quarter of 2016.

“We are pleased to report our second quarter earnings, for the first time as a public company, following the successful completion of our initial public offering and listing on the New York Stock Exchange on June 30, 2017,” said Alberto Paracchini, President and Chief Executive Officer of Byline Bancorp, Inc. “The capital raised through our IPO will allow us to continue growing the Byline franchise and increase our market share among small businesses and middle-market companies in the markets we serve. We believe this a very exciting time for Byline. Our second quarter results reflect the positive impact of our efforts over the past year to drive revenue growth and improve efficiencies. Compared to the second quarter of 2016, our total revenues increased by more than 60% while our efficiency ratio improved to 66.23% from 83.03%. As a result, we were able to deliver a 136.2% year-over-year increase in net income.

“Our new loan and lease production has steadily increased throughout the first half of the year and that momentum has carried over into the third quarter. Our pipelines remain strong across all of our teams which should result in stronger balance sheet growth for the second half of the year. As we continue to attract new customers and talented bankers, add quality assets and leverage our strong core deposit base, we anticipate generating a steady increase in our level of profitability and creating long-term value for our stockholders,” said Mr. Paracchini.

As previously disclosed, during the second quarter of 2017 and in connection with the Company’s initial public offering, the Company agreed to repurchase all $15.0 million of its outstanding shares of Series A Preferred Stock for $25.5 million. The $10.5 million excess of the consideration paid over the $15.0 million carrying amount of the Series A Preferred Stock was treated as a one-time dividend declaration on the Series A Preferred Stock in accordance with applicable accounting guidance. Both the dividend declared on the Series A Preferred Stock and the regular quarterly dividend paid on the Series B Preferred Stock are reflected in the reported net loss attributable to common stockholders for the second quarter of 2017, which was $4.6 million, or $0.18 per common share. The one-time impact of the Series A Preferred stock repurchase was $0.42 per diluted common share.

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Net Interest Income    

Net interest income for the second quarter of 2017 was $29.8 million, compared with $29.5 million for the first quarter of 2017. The increase in net interest income was due primarily to an increase in accretion income attributable to the acquired purchased credit impaired loans in our portfolio and an increase in loan yields stemming from rising interest rates. The increase in accretion income was driven by an improvement in the expected future performance of the acquired purchase credit impaired loans in the portfolio.

Relative to the second quarter of 2016, net interest income increased 46.3%. The increase was primarily attributable to organic growth in the loan and lease portfolio and the impact of the Ridgestone Financial Services, Inc. acquisition completed in October 2016.

Net Interest Margin

Net interest margin for the second quarter of 2017 was 4.02%, up 2 basis points from the first quarter of 2017. Net interest margin for the second quarter of 2017 increased due to additional accretion income and increased earning asset yields due to the rise in short term interest rates during the quarter. This was offset by increases in the cost of interest bearing liabilities.

Relative to the second quarter of 2016, the net interest margin increased from 3.41%, primarily due to an increase in accretion income and a favorable shift in the mix and yield of earning assets.

Non-interest Income

Non-interest income for the second quarter of 2017 was $13.2 million, an increase of 7.2% from $12.3 million for the first quarter of 2017. The increase was primarily due to higher gain on sale income and servicing income.

The Company’s net gain on sales of government guaranteed loans is generated through its Small Business Capital (SBC) group which was established in conjunction with the acquisition of Ridgestone Financial Services, Inc.

During the second quarter of 2017, the Company recognized $8.3 million in net gains on sales of government guaranteed loans, compared to $8.2 million for the first quarter of 2017. The increase was attributable to a higher average net premium on sales of government guaranteed loans. During the second quarter of 2017, the Company sold $75.1 million of government guaranteed loans compared to $76.5 million in the first quarter of 2017.

Non-interest income increased 112.9% from $6.2 million in the second quarter of 2016. The increase was primarily attributable to net gains on sales of government guaranteed loans and associated servicing fees resulting from the acquisition of Ridgestone Financial Services, Inc.

Non-interest Expense

Non-interest expense for the second quarter of 2017 was $29.2 million, compared with $28.9 million for the first quarter of 2017, a 1.0% increase. Compared to the prior quarter, the most significant variances included a $711,000 increase in other real estate owned expenses primarily due to a reduction in the

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net gain on sales of other real estate owned, a $624,000 increase in salaries and employee benefits expense associated with an increase in lending personnel during the quarter, which was partially offset by a $581,000 decrease in professional fees. When compared to the second quarter 2016, non-interest expense increased by $6.4 million primarily due to personnel and operating expenses added as a result of the Ridgestone Financial Services, Inc. acquisition.

The Company’s efficiency ratio was 66.23% in the second quarter of 2017, compared with 67.11% in the first quarter of 2017 and 83.03% in the second quarter of 2016. The improvement in efficiency ratio from the prior periods is primarily attributable to higher revenues resulting from the acquisition of Ridgestone Financial Services, Inc. and organic loan and lease growth, combined with cost savings recognized from branch consolidations in 2016.

Loan and Lease Portfolio

Total loans and leases held for investment were $2.1 billion at June 30, 2017, an increase of $5.9 million from March 31, 2017. The Company’s originated loan and lease portfolio increased by $154.8 million during the second quarter of 2017, which was offset by $148.9 million of net run-off in the portfolio. The growth in the originated loan and lease portfolio was primarily driven by increases in commercial real estate loans, government guaranteed lending, and leases.

During the first half of the year we experienced a higher than anticipated level of run-off in our loan portfolio driven by several commercial real estate construction projects achieving stabilization, refinancing activity in syndicated credits where we opted not to participate in the new facility and a commercial loan that paid off in full.

Deposits

Total deposits were $2.5 billion at June 30, 2017, compared with $2.6 billion at March 31, 2017. The deposit mix changed slightly with non-interest bearing demand deposits increasing by $49.4 million offset by a decrease in municipal deposits subject to seasonality and run-off in the time deposits acquired as part of the Ridgestone acquisition. The increase in non-interest bearing deposits was driven by new deposit relationships and loan fundings that occurred at the end of the quarter. Non-interest bearing deposits accounted for 30.8% of total deposits for the second quarter versus 28.4% in the first quarter. Core deposits remained stable at 84.9% of total deposits at June 30, 2017.

Asset Quality

Non-performing assets totaled $29.0 million, or 0.86% of total assets, at June 30, 2017, an increase from $22.0 million, or 0.67% of total assets, at March 31, 2017. The increase in non-performing assets during the second quarter of 2017 was primarily due to an increase in nonaccrual loans of $7.4 million primarily in the government guaranteed loan portfolio, partially offset by a decrease in other real estate owned of $489,000.

The increase in nonaccrual loans for the quarter was driven primarily by two commercial loans. One of the loans is a government guaranteed loan carrying an 80% government guaranty and the other is fully secured by cash.

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Net charge-offs for the second quarter of 2017 were $1.4 million, or 0.26% of average loans and leases, on an annualized basis, compared to $1.0 million, or 0.19%, for the first quarter of 2017, and $2.6 million, or 0.68%, for the second quarter of 2016.

The Company recorded a provision for loan and lease losses of $3.5 million for the second quarter of 2017, compared to $1.9 million for the first quarter of 2017, and $1.2 million for the second quarter of 2016, reflecting growth in the loan and lease portfolio and net impairment of certain acquired loans based on a periodic update of expected loan cash flows. The updated estimates of expected loan cash flows on acquired loans also resulted in the reclassification of approximately $15.4 million of non-accretable yield to accretable yield that will be prospectively recognized over the estimated life of the loans.

The Company’s allowance for loan and lease losses was 0.65% of total loans and leases and 85.85% of non-performing loans and leases at June 30, 2017, compared to 0.55% and 133.57%, respectively, at March 31, 2017. The reduction in the ratio was driven by the increase in nonaccrual loans. The acquisition accounting adjustment on acquired loans was $37.7 million and $41.0 million at June 30, 2017 and March 31, 2017, respectively.

Capital

At June 30, 2017, the Company exceeded all applicable regulatory capital requirements under Basel III, as summarized in the following table:

Conference Call, Webcast and Slide Presentation

The Company will host a conference call and webcast at 9:00 a.m. Central Time on Friday, July 28, 2017 to discuss its quarterly financial results. The call can be accessed via telephone at (888) 317-6016. A recorded replay can be accessed through August 11, 2017 by dialing (877) 344-7529; passcode: 10110708.

A slide presentation relating to the second quarter 2017 results will be accessible prior to the scheduled conference call. The slide presentation and webcast of the conference call can be accessed on the Events and Presentations page of the Company’s investor relations website at www.bylinebancorp.com.

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About Byline Bancorp, Inc.

Headquartered in Chicago, Byline Bancorp, Inc. is the holding company for Byline Bank, a full service commercial bank serving small- and medium-sized businesses, financial sponsors, and consumers. Byline Bank had $3.3 billion in assets at June 30, 2017, and operates more than 50 full service branch locations throughout the Chicago and Milwaukee metropolitan areas. Byline Bank offers a broad range of commercial and retail banking products and services including small ticket equipment leasing solutions and is one of the top 10 Small Business Administration lenders in the United States.

Non-GAAP Financial Measures

This release contains certain financial information determined by methods other than in accordance with accounting principles generally accepted in the United States of America (“GAAP”). These measures include non-interest income to total revenues, pre-tax pre-provision return on average assets, tangible book value per share and tangible common equity to tangible assets. Management believes that these non-GAAP financial measures provide useful information to management and investors that is supplementary to the Company’s financial condition, results of operations and cash flows computed in accordance with GAAP; however, management acknowledges that our non-GAAP financial measures have a number of limitations. As such, these disclosures should not be viewed as a substitute for results determined in accordance with GAAP financial measures that other companies use. Management also uses these measures for peer comparison. See “Reconciliation of Non-GAAP Financial Measures” in the financial schedules included in this press release for a reconciliation of the non- GAAP financial measures to the comparable GAAP financial measures.

Non-interest income to total revenues is non-interest income divided net interest income plus non-interest income. Management believes that it is standard practice in the industry to present non-interest income as a percentage of total revenue. Accordingly, management believes providing these measures may be useful for peer comparison.

Pre-tax pre-provision return on average assets is pre-tax income plus the provision for loan and lease losses, divided by average assets. Management believes this metric is important due to the tax benefit resulting from the reversal of the net deferred tax asset valuation allowance and demonstrates profitability excluding the tax benefit and excludes the provision for loan and lease losses.

Tangible book value per share is calculated as tangible common equity divided by total shares of common stock outstanding. Management believes this metric is important due to the relative changes in the book value per share exclusive of changes in intangible assets.

Tangible common equity to tangible assets is calculated as tangible common equity divided by tangible assets. Management believes this measure is important to investors and analysts interested in relative changes in the ratio of total stockholders’ equity to total assets, each exclusive of changes in intangible assets.

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Forward-Looking Statements

This communication contains forward-looking statements within the meaning of the U.S. federal securities laws. Forward-looking statements include, without limitation, statements concerning plans, estimates, calculations, forecasts and projections with respect to the anticipated future performance of the Company. These statements are often, but not always, made through the use of words or phrases such as “may”, “might”, “should”, “could”, “predict”, “potential”, “believe”, “expect”, “continue”, “will”, “anticipate”, “seek”, “estimate”, “intend”, “plan”, “projection”, “would”, “annualized”, “target” and “outlook”, or the negative version of those words or other comparable words or phrases of a future or forward-looking nature. Forward-looking statements reflect various assumptions and involve elements of subjective judgement and analysis, which may or may not prove to be correct, and which are subject to uncertainties and contingencies outside the control of Byline and its respective affiliates, directors, employees and other representatives, which could cause actual results to differ materially from those presented in this communication. No representations, warranties or guarantees are or will be made by Byline as to the reliability, accuracy or completeness of any forward-looking statements contained in this communication or that such forward-looking statements are or will remain based on reasonable assumptions. You should not place undue reliance on any forward-looking statements contained in this communication. Forward-looking statements speak only as of the date they are made, and we assume no obligation to update any of these statements in light of new information, future events or otherwise unless required under the federal securities laws.

Contacts:

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CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (unaudited)

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CONSOLIDATED STATEMENTS OF OPERATIONS (unaudited)

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CONSOLIDATED FINANCIAL SUMMARY (unaudited)    

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CONSOLIDATED FINANCIAL SUMMARY (unaudited) (continued)    

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COMPOSITION OF LOANS, LEASES AND DEPOSITS (unaudited)

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RECONCILIATIONS OF NON-GAAP FINANCIAL MEASURES (unaudited)

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NET INTEREST MARGIN (unaudited)

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NET INTEREST MARGIN (unaudited)(continued)

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NET INTEREST MARGIN (unaudited)(continued)