The Aegis-owned Diffinti beat WWP's MediaCom, Havas' Media Contacts and Syzergy's Unique Digital to land the business, which is one of the largest online media accounts in the UK.
The account includes Sky's online display and affiliate activity. Diffiniti already handles Sky's search engine optimisation business, which it won in 2007.
Nigel Sharrocks, the chief executive of Aegis Media, worked with the Diffiniti managing director Rob Horler, in the pitch. Unique Digital retains Sky's paid-for search and MediaCom remains as Sky's offline agency.
I-level won Sky's digital display and search account in 2005. But the broadcasting giant repitched its search account in August 2007, and terminated its relationship with the agency in December.
I-level also lost its AA £22 million search-based online ad account in October 2007 after two years.