Exhibit 99.1

Integral Ad Science Reports Second Quarter 2021 Financial Results

Total revenue increased 55% year-over-year to $75.1 million; programmatic revenue increased 94% to $31.8 million

NEW YORK – August 12, 2021 – Integral Ad Science Holding Corp. (“IAS”) (Nasdaq: IAS), a global leader in digital media quality, today announced financial results for the second quarter ended June 30, 2021.

“IAS delivered record performance in the second quarter driven by continued growth in both advertiser direct and programmatic revenue. We also achieved a significant milestone this quarter with our successful IPO, advancing our position as the global benchmark for trust and transparency in digital media quality,” said Lisa Utzschneider, CEO of IAS. “More customers are partnering with IAS to make every impression count in key growth areas including programmatic, social, connected TV (CTV), and international markets. Earlier this week, we announced our acquisition of Publica, the CTV advertising platform. By acquiring Publica, we are demonstrating our commitment to leading the future of digital media quality in CTV.”

Second Quarter 2021 Financial Highlights

Recent Business Highlights

Financial Outlook

“Our investments in product innovation and international growth are delivering results for our customers and contributed to our strong performance in the second quarter,” said Joe Pergola, CFO of IAS. “Our three revenue streams posted solid growth with programmatic representing 42% of total second quarter revenue compared to 34% in the prior-year-period. Moving forward, we expect to further develop our high-growth areas and expand our global footprint while maintaining strong profitability.”

IAS is introducing the following financial guidance for the third quarter of 2021 and full year, which includes the anticipated contribution from the Publica acquisition:

Quarter Ending September 30, 2021:

Year Ending December 31, 2021:

Integral Ad Science Holding Corp.

Condensed Consolidated Balance Sheets

(Unaudited)

Integral Ad Science Holding Corp.

Condensed Consolidated Statements of Operations and Comprehensive Loss

(Unaudited)

Integral Ad Science Holding Corp.

Condensed Consolidated Statements of Changes in Members’/Stockholders’ Equity

(Unaudited)

Three Months Ended June 30, 2021

Integral Ad Science Holding Corp.

Consolidated Statement of Cash Flows

(Unaudited)

Supplemental Disclosure Regarding Non-GAAP Financial Information

We use supplemental measures of our performance, which are derived from our consolidated financial information, but which are not presented in our consolidated financial statements prepared in accordance with GAAP. Adjusted EBITDA is the primary financial performance measure used by management to evaluate our business and monitor ongoing results of operations. Adjusted EBITDA is defined as earnings (loss) before depreciation and amortization, stock-based compensation, interest expense, benefit from income taxes, acquisition, restructuring and integration costs and IPO readiness costs. Adjusted EBITDA margin represents the Adjusted EBITDA for the applicable period divided by the revenue for that period presented in accordance with GAAP.

We use non-GAAP financial measures to supplement financial information presented on a GAAP basis. We believe that excluding certain items from our GAAP results allows management to better understand our consolidated financial performance from period to period and better project our future consolidated financial performance as forecasts are developed at a level of detail different from that used to prepare GAAP-based financial measures. Moreover, we believe these non-GAAP financial measures provide our shareholders with useful information to help them evaluate our operating results by facilitating an enhanced understanding of our operating performance and enabling them to make more meaningful period-to-period comparisons. Although we believe these measures are useful to investors and analysts for the same reasons, they are useful to management, as discussed below, these measures are not a substitute for, or superior to, U.S. GAAP financial measures or disclosures.

IAS is unable to provide a reconciliation for forward-looking guidance of Adjusted EBITDA to net income (loss), the most closely comparable GAAP measure, because certain material reconciling items, such as depreciation and amortization, stock-based compensation, interest expense, income tax expense (benefit) and acquisition, restructuring and integration expenses, cannot be estimated due to factors outside of IAS’s control and could have a material impact on the reported results. Accordingly, a reconciliation is not available without unreasonable effort.

Reconciliation of Adjusted EBITDA to its most directly comparable GAAP financial measure, net loss, is presented below. We encourage you to review the reconciliations in conjunction with the presentation of the non-GAAP financial measures for each of the periods presented. In future fiscal periods, we may exclude such items and may incur income and expenses similar to these excluded items.

Reconciliation of Adjusted EBITDA

Operating Expenses Excluding Stock-Based Compensation

(Non-GAAP)

Conference Call and Webcast Information

IAS will host a conference call and live webcast to discuss itssecond quarter 2021 financial results today at 5:00 p.m. ET. To access the conference call, please dial US/Canada Toll-Free: 877-313-2138 International: 470-495-9538 Conference ID: 9609315 The webcast will beavailable live on IAS’s investor relations website: https://investors.integralads.com. A replay will be available following the conclusion of the call.

About Integral Ad Science

Integral Ad Science (IAS) is a global leader in digital media quality. IAS makes every impression count, ensuring that ads are viewable by real people, in safe and suitable environments, activating contextual targeting, and driving supply path optimization. Our mission is to be the global benchmark for trust and transparency in digital media quality for the world’s leading brands, publishers, and platforms. We do this through data-driven technologies with actionable real-time signals and insight. Founded in 2009 and headquartered in New York, IAS works with thousands of top advertisers and premium publishers worldwide. For more information, visit integralads.com.

Forward-Looking Statements

This earnings press release contains forward-looking statements that are subject to risks and uncertainties. All statements other than statements of historical fact included in this press release are forward-looking statements. Forward-looking statements give our current expectations and projections relating to our financial condition, results of operations, plans, objectives, future performance and business. You can identify forward-looking statements by the fact that they do not relate strictly to historical or current facts. These statements may include words such as “anticipate,” “estimate,” “expect,” “project,” “plan,” “intend,” “believe,” “may,” “will,” “should,” “can have,” “likely,” and other words and terms of similar meaning in connection with any discussion of the timing or nature of future operating or financial performance or other events. For example, all statements we make relating to our estimated and projected costs, expenditures, cash flows, growth rates and financial results or our plans and objectives for future operations, growth initiatives, or strategies are forward-looking statements. All forward-looking statements are subject to risks and uncertainties that may cause actual results to differ materially from those that we expected, including: (i) the adverse effect on our business, operating results, financial condition, and prospects from the current COVID-19 pandemic and related economic downturns; (ii) our dependence on the overall demand for advertising; (iii) our dependence on the overall demand for advertising; (iv) a failure to innovate or make the right investment decisions; (v) our failure to maintain or achieve industry accreditation standards; (vi) our ability to compete successfully with our current or future competitors in an intensely competitive market; (vii) our dependence on integrations with advertising platforms, demand-sideproviders (“DSPs”) and proprietary platforms that we do not control; (viii) our international expansion; (ix) our ability to expand into new channels; (x) our ability to sustain our profitability and revenue growth rate decline; (xi) risks that

our customers do not pay or choose to dispute their invoices; (xii) risks of material changes to revenue share agreements with certain DSPs; (xiii) the impact that any future acquisitions, strategic investments, or alliances may have on our business, financial condition, and results of operations; (xiv) interruption by man-made problems such as terrorism, computer viruses, or social disruption impacting advertising spending; and (xv) other factors disclosed in the section entitled “Risk Factors” Prospectus filed with the SEC on July 1, 2021 in connection with our initial public offering. Given these factors, as well as other variables that may affect our operating results, you should not rely on forward-looking statements, assume that past financial performance will be a reliable indicator of future performance, or use historical trends to anticipate results or trends in future periods.

We derive many of our forward-looking statements from our operating budgets and forecasts, which are based on many detailed assumptions. While we believe that our assumptions are reasonable, we caution that it is very difficult to predict the impact of known factors, and it is impossible for us to anticipate all factors that could affect our actual results. The forward-looking statements included in this press release are made only as of the date hereof. We undertake no obligation to update or revise any forward-looking statement as a result of new information, future events or otherwise, except as otherwise required by law.

Investor Contact:

Lally Zirkle

Investor Relations at IAS

Jonathan Schaffer and Cameron Felton

The Blueshirt Group, for IAS

ir@integralads.com

Media Contact:

Julie Nicholson

jnicholson@integralads.com