 In his first bid, for elective office, McGrath was elected as a Democrat to the Eighty-ninth Congress, defeating four-term Republican Party incumbent Milton W. Glenn.He served in office from January 3, 1965 to January 3, 1967, and was an unsuccessful candidate for reelection in 1966 to the Ninetieth Congress.After leaving Congress, McGrath was general counsel at the Department of Housing and Urban Development from 1967–1969; Treasurer of the New Jersey Democratic State Committee from 1969 to 1973 and a consultant in the construction and finance industry from 1969-1992.