Perhaps best known for his supporting roles in such classic 1960s films as Midnight Cowboy, Breakfast at Tiffany's, and The Manchurian Candidate, McGiver also appeared in episodes of The Twilight Zone, Alfred Hitchcock Presents, and The Patty Duke Show, as well as in a series of American Express commercials.
After earning a bachelor's degree from Fordham University and graduate degrees from both Catholic University and Columbia University, he taught English classes and performed in productions at New York City's Irish Repertory Theater. After serving in the United States Army during World War II, he continued his teaching and acting careers.
In the mid-1960s, he played the role of Walter Burnley on the CBS comedy series Many Happy Returns.
He grew up in New York City as the child of Irish-born parents. His three-decade marriage to Ruth Schmigelsky resulted in ten children.
He appeared with Paula Prentiss and Rock Hudson in the 1964 film Man's Favorite Sport?