International revenue climbed 9.3% to $1.33bn, while domestic revenue rose 3.9% to $1.59bn. Reports put the company's organic growth figure at 2.1%.
However, net income slipped by 0.6% to $163.4m (£106.2m).
The group, which owns agency networks such as DDB, BBDO and OMD, saw its share price rise to a 12-month high of $43.91 after its results release.
John Wren, chief executive, said on a conference call: "The general business environment continues to stabilise and improve and, as we look at individual countries and regions, we are cautiously optimistic about continued growth."
The US group's results follow , which showed a 1.5% year-on-year rise in organic growth.
Omnicom's close rival WPP is set to reveal its first quarter figures on 30 April.
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