From 1968 to 1970, John J. Cavanaugh served in the United States Army. In 1972 he was elected to the Nebraska unicameral and served until 1976, when he was elected to represent Nebraska’s 2nd district in the 95th United States Congress. He was re-elected to the 96th United States Congress serving from January 3, 1977 to January 3, 1981. Cavanaugh did not run for reelection in 1980, instead resuming his law practice in Omaha where he currently resides. He was a delegate for Nebraska to the Democratic National Convention of 1980, 2000, and 2004.