 He was a delegate to the New Jersey Constitutional convention in 1966 and selected as a delegate to the 1968 Republican National Convention.Forsythe was elected simultaneously as a Republican to the 91st and to the 92nd Congress by special election to fill the vacancy caused by the resignation of United States Representative William T. Cahill, and reelected to the seven succeeding Congresses (November 3, 1970 – March 29, 1984).Forsythe represented New Jersey's 6th congressional district until 1983.