While revenues were down 0.8% to $1.16bn in the US for the owner of McCann and FCB, the drop was more pronounced across its international business, falling 1.3% to $746.6m.
However, profit (reported as net income) for the three months ending 30 September was $148.8m, up 12.1% from $132.7m in 2016.
Organic revenue was up 0.5% in Q3 compared with 2016, with the US's strong performance (up 1.3%) offset by a weaker international performance (down 0.7%). The UK experienced organic growth of 3%, with continental Europe and Interpublic's "other markets group" also enjoying growth, while Asia-Pacific and Latin America decreased.
Michael Roth, IPG's chairman and chief executive, said that while the results reflected "strong operating margin expansion", macro economic trends and cautious clients were having an adverse impact on performance.
For the first nine months of 2017, total revenues were down a marginal 0.7% to $5.54bn, thanks mostly to a 2% fall in international revenue. Net profit was down from $295.6m in the first nine months of 2016 to $261.5m this year.
"Our agencies and our talent across the portfolio remain among the best in their respective disciplines, which gives us confidence in the long-term competitiveness of our offerings and our client-centric service model," Roth said.
Interpublic houses creative agencies including McCann Worldgroup, MullenLowe and FCB, and media agencies under the IPG Mediabrands umbrella.