 Sosman was born in Boston in 1950 and grew up in Concord.Sosman graduated from Concord-Carlisle Regional High School in 1968, from Middlebury College "cum laude" in 1972, and from the University of Michigan Law School "magna cum laude" in 1979.Sosman worked as an attorney with Foley, Hoag & Eliot in Boston from 1979 to 1984 before becoming an Assistant U.S. Attorney for two years.