As European managing director of Marin, Stevenson will lead the London office and the expansion into Europe the company plans later this year.
He is currently recruiting "big name" figures from the search industry.
Since launching in the US in 2007 Marin has grown to handle in excess of $300m of annual search spend for more than 100 companies.
The company is focused on helping marketers and agencies make their search engine marketing more efficient.
Stevenson is also the former managing director of 24/7 Real Media. He said: "The growth of the search industry has charged ahead in the last few years, and too many search marketers and agencies have kept their heads above water by employing an army of junior staff to keep things ticking over.
"This is clearly not a long term solution and we're at the point where profitability and client satisfaction are taking a hit."
Its arrival was welcomed by Jim Brigden, the chief executive of the fastest-growing search marketing agency in the UK, I Spy Search, who praised "its ability to eliminate complexity and cut costs in search campaigns".