He became friends with John Cassavetes and Peter Falk at the Actors Studio in his native New York City.
He served in the United States Navy during World War II.
Made thirteen appearances in the Columbo (1971) series. He is one of a few actors, besides Peter Falk, to play the same character in more than one adventure/episode.
He was one of 11 children born to Irish immigrant parents.
Finnegan appeared in five films of director/actor John Cassavetes.