Justin Charles Garrett Leonard (born June 15, 1972) is an American professional golfer.

Leonard was born and raised in Dallas, Texas. He attended Lake Highlands High School and graduated in 1990. He attended the University of Texas at Austin and was the individual NCAA champion in 1994. He won the 1992 U.S. Amateur and was a two-time All-American in 1993 and 1994. He won the Haskins Award in 1994 as the most outstanding collegiate golfer. That same year Leonard became only the fourth golfer to go directly from college to the PGA Tour without going through Q School, after Gary Hallberg, Scott Verplank, and Phil Mickelson.

Leonard's wins on the PGA Tour included one of golf's four majors, the 1997 Open Championship, as well as the 1998 Players Championship. He ranked in the top 10 of the Official World Golf Ranking for 24 weeks in 1998 and 1999. Leonard also had opportunities to win other major championships, notably at the 1999 Open Championship and the 2004 PGA Championship; in both instances he fell into a playoff with a bogey on the 72nd hole.

At the 1997 PGA Championship, Leonard was tied with Davis Love III for the 54-hole lead. Love shot a final round 66 to win by five shots over Leonard, who finished solo second. Leonard was ahead by three shots at the 54-hole mark of the 2002 PGA Championship before shooting a final round 77 and finishing tied for fourth.

Leonard qualified for the United States Ryder Cup team in 1997, 1999, and 2008. In the 1999 event, Leonard made a 45-foot putt for birdie on the 17th hole to complete a remarkable comeback by the U.S. team on the final day. The victory was somewhat marred by the celebration following Leonard's putt, when other U.S. players, their wives, and a few fans ran onto the green even though Leonard's opponent, José María Olazábal, still had an opportunity to match Leonard on the hole.