One by AOL was founded as Millennial Media in May 2006 by Paul Palmieri and Chris Brandenburg.

In January 2012, Millennial Media filed with the SEC for an initial public offering of its common stock,[9] and the company was first listed in March 2012.

[9] On January 27, 2014, Palmieri stepped down from his position and was replaced by Michael Barrett.

[10] On September 3, 2015, AOL agreed to buy Millennial Media for US$238 million.

[12] On September 10, 2018, AOL's parent company Oath 'combined' BrightRoll, One by AOL and Yahoo Gemini into a single advertising proposition dubbed Oath Ad Platforms.