Irwin graduated from the University of Colorado in 1967, where he was a two-time All-Big Eight defensive back, as well as an academic All-American in football. He won the individual NCAA Division I Championship in golf in 1967 and turned professional the following year.

Irwin had 20 victories on the PGA Tour beginning with the 1971 Sea Pines Heritage Classic and finishing with the 1994 MCI Heritage Golf Classic, and won prize money of just under six million dollars. His three major championship titles were the 1974, 1979, and 1990 US Opens. His 1998 win at the U.S. Senior Open came at the Riviera Country Club.

Irwin qualified to play on the over 50s Champions Tour (formerly the Senior PGA Tour) in 1995 and has enjoyed even greater success at this level than he did on the PGA Tour. He has won over 65 Champions Tour events.