The pair join from Fallon's New York office, which closed in July. Sheahan, 28, an art director, and Senn, 28, a copywriter, were responsible for the "pendulum" poster execution for Time magazine that took a gold Lion at Cannes and a silver Pencil at this year's D&AD awards. The pair also worked on accounts including Virgin Mobile, Starbucks and Timberland.
The Fallon creative director, Andy McLeod, said: "Molly and Marty are undoubtedly one of New York's brightest young teams and we are really looking forward to having them in our creative department."
Senn joined Fallon New York in 2003 from Publicis in the West in Seattle, where he worked on accounts including T-Mobile, the Washington Lottery and Safeco Insurance. Before that, he worked at Mullen on accounts such as Nextel and Dexter shoes.
Sheahan moved to Fallon's New York office from Lowe New York, where she worked on the RCA, Johnson & Johnson and Milk accounts.