Murphy was admitted to the bar and commenced the practice of law in Portsmouth in 1955.

Murphy was legal counsel to the New Hampshire Senate in 1957–1958, and administrative assistant to Governor Wesley Powell from 1959 to 1961.

Powell's choice of Murphy was controversial; powerful publisher William Loeb published a front-page editorial in the Manchester Union Leader attacking Powell for passing over the late Senator's widow Doloris.

[9] Governor Powell, too, was defeated in that primary, and in his election night speech, he referenced Loeb's opposition and added that "I'm paying the penalty for appointing a Catholic to the U.S.

"[9] Murphy later served on the Portsmouth Economic Commission, Portsmouth Housing Authority and was elected chairman of the board of the Portsmouth-Kittery Armed Services Committee (now called the Seacoast Shipyard Association).

He was chairman of the board and general counsel of the Portsmouth (N.H.) Savings Bank from 1968 to 1988.