From 1968 to 1970 he served in the United States Army. In 1972 he was elected to the Nebraska Legislature and served until 1976 when he was elected to represent Nebraska's 2nd district in the Ninety-fifth United States Congress. He was reelected to the Ninety-sixth United States Congress serving from January 3, 1977 to January 3, 1981. He did not run for reelection in 1980, opting to resume his practice in Omaha. He is a Catholic and was a delegate for Nebraska to the Democratic National Convention of 1980, 2000, and 2004. Cavanaugh is a member of the ReFormers Caucus of Issue One.