The group behind creative agencies DDB and BBDO, and media networks OMD and PHD, grew worldwide revenues by 7.9% to $3.15bn.
Overall organic growth was 5.2%, which was outstripped by the UK's 9.1% rise.
One of Omnicom's big UK wins during the year was the £70m creative account for Virgin Media, which went to DDB and Rapp in May.
In 2010, Omnicom increased net income by 4.4% to $827.7m and revenue by 9% to $12.5bn.
Omnicom is the first of the holding companies to report its first-quarter results, with Publicis Groupe expected to reveal its numbers on Thursday.