The company's total revenues were up 11.2% year-on-year to $3.48bn, but its domestic and international divisions are running at different speeds.
International revenues surged 17.7% to $1.73bn, coming close to overtaking domestic revenues, which increased 5.5% to $1.75bn.
The decline of the US dollar over the 12-month period flatters international revenues.
Omnicom is headed by president and chief executive John Wren and owns agency networks including media specialists OMD and PHD; advertising specialists DDB and BBDO; and PR agencies Ketchum and Porter Novelli.