NEW YORK — Online company AOL is buying highly-trafficked website Huffington Post in a $315 million deal that represents a big bet on the future of online news.

The acquisition, which will put Huffington Post co-founder Arianna Huffington in charge of all AOL content, brings AOL an additional 25 million unique visitors a day.

That could help AOL begin to turn around its display advertising business, which has struggled to grow as the company tries to turn itself into a content provider and moves farther away from its roots providing dial-up Internet.

The deal “will create a next-generation American media company with global reach that combines content, community, and social experiences for consumers,” AOL CEO Tim Armstrong said in a statement announcing the deal early today.

Founded in 2005, Huffington Post is owned by Arianna Huffington, Kenneth Lerer and a group of other investors. AOL will pay $300 million of the purchase price in cash.

Arianna Huffington will be named president and editor-in-chief of The Huffington Post Media Group, which will include all Huffington Post and AOL content, including Engadget, TechCrunch, MapQuest, Patch and more.