What is the biggest marketing agency in the US?
The biggest US-headquartered marketing/advertising agencies by revenue are inside the Omnicom Group (BBDO, TBWA, DDB, PHD) and Interpublic Group (McCann, IPG Mediabrands). Individual brands within these holding groups regularly bill $500M–$1B+ annually. Ogilvy (WPP), Wieden+Kennedy (independent), and R/GA (Interpublic) round out the top of the US market.
Why this matters
This question shows up regularly in Google's People Also Ask for the "marketing agency" query, which is a signal that buyers in this space are asking it constantly during their research phase. The answer above is written from The Wall's editorial position — we index 2,286 verified US growth-services vendors across 10 pillars and see how these questions map to actual buying decisions.
If you're evaluating vendors in this category, the Marketing pillar page has the full US firm list with rates, team sizes, and headquarters filters.