Forsythe was born in Westtown Township, Pennsylvania on January 17, 1916, and attended the local public schools.

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 to become Governor of New Jersey, and reelected to the seven succeeding Congresses (November 3, 1970 – March 29, 1984).

In redistricting following the 1980 United States census, Forsythe was shifted to New Jersey's 13th congressional district, where he was elected for a single term in office.

Forsythe died at the age of 68 at his home in Moorestown Township on March 29, 1984, due to lung cancer.

[1] His remains were cremated and his ashes interred at Union Street Friends Cemetery, Medford, New Jersey.