Stadler displayed early skill at golf, and won the 1973 U.S. Amateur, and attended the University of Southern California where he became a two-time All-American.

Very popular with the galleries, Stadler is known as "The Walrus" among golf circles. He turned professional in 1975, and won the 1982 Masters. He won his first two PGA Tour wins in 1980, at the Bob Hope Desert Classic and the Greater Greensboro Open. He also won four more tournaments in 1982, including the first of his two World Series of Golf titles.

He won the Byron Nelson Golf Classic in 1984, and the 1991 Tour Championship. He won the World Series of Golf again in 1992, and the Buick Invitational of California in 1994. He also won the Nissan Open in 1996 and the B.C. Open in 2003, becoming one of the oldest players to win on the PGA Tour. He won 13 PGA Tour events in total.

Stadler began playing the Champions Tour upon becoming eligible in June 2003, and was the leading money winner in his first full year on that tour in 2004.