Refinery boasts Merck, Campbells, Merrill Lynch and Amgen on its client roster, and employs 79 people in its Philadelphia headquarters.
Refinery will be integrated with G2's digital marketing business unit, G2 Interactive, operating under the leadership of its president, John Paulson.
Joe Celia, chairman and CEO at G2 Worldwide, said: "In today's market it is not enough to excel at strategy and creative, but we have to be able to deliver the goods in technology, analytics and operational excellence too.
"By combining Refinery's best-in-class capabilities in these areas, with G2's digital marketing expertise, we will provide clients with a new level of excellence in end-to-end interactive marketing services."
G2, which is part of Grey Global, currently has 86 offices in 42 countries and has been rapidly expanding in recent months. Its latest acquisitions include Star Echo, a marketing agency in China, and MDS Boole, a data company in Spain.
This year G2 has won new business with Campbell's and Canon in North America; with Visa for the Olympics in Asia; and with The Coca-Cola Company throughout Europe.