Carrigan, who is also a managing partner of the direct marketing company OgilvyOne, is to be replaced with immediate effect by Louise Ainsworth, who has been appointed a managing partner.
Carrigan was key in the growth of OgilvyInteractive in the UK after his new-media company, NoHo Digital, was acquired by WPP in 1999 during the dotcom boom to drive the development of its digital operation.
NoHo was established by Carrigan in 1994 and, at the time of acquisition, employed 30 staff and meant that OgilvyInteractive picked up clients including Virgin, Microsoft, Prudential and Unilever.
He has also worked for the publisher Emap, where he was part of the launch team for Multimedia Magazine. He was the editor until 1992.
He said his plans were not yet fixed but that he was considering launching a start-up.
His replacement Ainsworth is currently the director of strategy and client development at OgilvyInteractive.
She joined in May this year from the now defunct Om-nicom-owned digital company Organic.
Ogilvy Interactive has a network of 15 European offices as part of its global presence, and multinational clients including IBM, American Express, GlaxoSmithKline, Nestle, BT and Ford.
The digital operation works as both an individual entity as well as the new-media arm of both the advertising agency Ogilvy & Mather and the direct marketing outfit OgilvyOne.