From 1960 to 1962, he served as an Assistant District Attorney in Manhattan, and from 1962 to 1974 he served as an Assistant District Attorney in Nassau County. In 1975, he was elected to the Nassau County District Court bench on the Republican and Conservative tickets. He was re-elected in 1980 on the Democratic, Republican, Conservative, and Liberal tickets. He was elected to the County Court of Nassau County in 1984, re-elected in 1994, and ran unsuccessfully for re-election in 2004 on the Republican and Conservative tickets. After leaving public service Belfi joined the Manhattan practice of Murray, Frank & Sailer LLP as senior counsel.