During his college years, he was the conference medalist in 1993, the year that the Midland College team dominated the Western Junior College Athletic Conference and won the regional title. In 1994, the Chaps repeated as WJCAC champions and finished second in the National Junior College Athletic Association championship. That year, Campbell was WJCAC medalist, Region V Tournament medalist and the NJCAA Tournament medalist runner-up. In 1994, he was named an NJCAA All-American. He was listed as the number one player in the final NJCAA national poll. After two years at Midland College, he won a scholarship and transferred to the University of Nevada-Las Vegas.

Prior to 2000, Campbell played on the third-tier NGA Hooters Tour, where he won 13 tournaments and was the leading money winner three times. Campbell left the tour as the career leader in wins and earnings. In 2001, he played on the second-tier Buy.com Tour, now known as the Web.com Tour, where he earned a "battlefield promotion," winning three tournaments to earn promotion to the elite PGA Tour part way through the season.

In 2003, Campbell won The Tour Championship, was runner-up to surprise winner Shaun Micheel at the PGA Championship, and finished seventh on the PGA Tour money list. He claimed a second PGA Tour win in 2004 and made a strong start to 2006, winning the Bob Hope Chrysler Classic and topping the money list for a short time early in the season. He won his fourth PGA Tour title by one stroke at the 2007 Viking Classic.

Campbell finished as a runner-up at the 2009 Masters, after losing in a three man sudden-death playoff, involving Ángel Cabrera and Kenny Perry. The three players had finished regulation play at 12-under par. At the first extra hole, Campbell hit his second shot from the middle of the fairway but found the greenside bunker. He played out of the bunker to four feet past the hole, but missed the par putt and was eliminated, as both Cabrera and Perry made pars. Earlier in the week, Campbell had made the best start to a Masters Tournament, after making five birdies in the first five holes.

Campbell played the 2013–14 season with conditional status, but failed to graduate from the Web.com Tour finals. He used a career money list exemption for 2014–15 and retained exempt status the following year.

Along with his wife, Amy, Campbell currently resides in the Fort Worth, Texas, area. Campbell is a supporter of several charitable causes and has been featured on PGA Tour commercials highlighting players giving back in the community. For his career, Campbell has accumulated over $17 million in total earnings.