Hart received a B.S.E. and M.S. from Princeton University and a J.D. from Harvard Law School. He was managing partner at the law firm of Hart & Chavers from 1981 to 1990 and associate attorney at Dickstein, Shapiro & Morin from 1979 to 1981. He served as the deputy assistant general counsel for environmental, civil rights, and general law at the Department of Transportation from 1977 to 1979.