Ad-verification firm Integral Ad Science Inc. has acquired Publica LLC, a technology company focused on internet-connected TV advertising, for $220 million, as deals heat up in the sector as well as ad-tech more broadly.

The purchase, paid for with 75% cash and 25% stock, is part of IAS’s ongoing strategy to diversify its portfolio and tap into products that marketers and publishers increasingly care about, such as those that support connected-TV advertising, said IAS Chief Executive Lisa Utzschneider.

Marketers will spend $13.4 billion on advertising in connected TV this year, research firm eMarketer estimates, as consumers spend more time watching TV and videos through connected devices.

“It’s the first inning of a long game in CTV,” Ms. Utzschneider said. “Where the consumers go, the marketers go, and given the tremendous consumer adoption in CTV, especially over the last 12 to 18 months of living this digital-first lifestyle, it just enables us to really accelerate that CTV opportunity.”

IAS, a New York-based company acquired by private-equity firm Vista Equity Partners in 2018, historically has worked largely with advertisers to help prove that their digital ads are viewable, meaning they aren’t running on parts of websites that can’t be seen. The business also helps marketers ensure their ads aren’t running on sites with objectionable content.

The latest deal will help the company expand its relationships with video publishers, said Ms. Utzschneider. It comes less than two months after the company listed on the Nasdaq Stock Market.

Publica, which is based in Palo Alto, Calif., supports media companies, including ViacomCBS Inc., Fox Corp. and streaming-TV company Philo Inc. The company’s technology manages and serves targeted ads for content that is streamed on connected TVs, as well as generating campaign analytics.

The Publica brand will become part of IAS’s product portfolio. Publica co-founder and CEO Ben Antier will report to Ms. Utzschneider.

The acquisition of Publica adds 30 employees to IAS’s 651 staffers. There are no layoffs planned as part of the deal, the company said.

IAS’s acquisition is the latest in a string of deals focused on advertising technology and connected TV. Last month Mediaocean LLC announced plans to acquire ad-server Flashtalking, while New Mountain Capital-backed Tinuiti Inc. acquired connected TV-focused ad-buying agency Bliss Point.

Write to Alexandra Bruell at alexandra.bruell@wsj.com