John Drayton Mahaffey, Jr. (born May 9, 1948) is an American professional golfer who has won numerous tournaments including 10 PGA Tour events.

Mahaffey was born in Kerrville, Texas. He attended the University of Houston in Houston, Texas. He turned pro in 1971 after graduating in 1970 with a degree in psychology.

Mahaffey came close to winning back to back U.S. Opens. In 1975 he lost in a playoff to Lou Graham at the Medinah Country Club in Medinah, Illinois. The following year Mahaffey had a two-shot lead after 54 holes at the Atlanta Athletic Club in Johns Creek, Georgia before shooting a final round 73 and finishing T4th.

In 1978, he won twice on the tour that year including one major, the PGA Championship. He also won the World Cup individual and team event where he was paired with Andy North that year.

The 1978 PGA championship was held at Oakmont Country Club in Oakmont, Pennsylvania. Mahaffey became the best comeback winner in PGA history after trailing Tom Watson by seven strokes with 14 holes to play. Ultimately, the tournament came down to a three-player playoff - Mahaffey, Watson and Jerry Pate. All three players made par on the first playoff hole. The drama ended on the second playoff hole when Pate missed the green, Watson missed a 30-foot birdie attempt and Mahaffey made his 12-foot birdie putt for the Championship.

Mahaffey played on the 1979 Ryder Cup team.

Mahaffey currently lives near Houston at The Woodlands in his home state of Texas. His family includes wife Elizabeth, son John D. III (born 1988) and daughter Meagan (born 1992). In his spare time, he enjoys fishing. Early in his career, Mahaffey was often sought out by other players to do comedic imitations for which he has a special talent. He last played on the Champions Tour in 2007. He works as a roving announcer on Champions Tour Golf Channel telecasts.