In 2006, he incurred a further four-year ban for testing positive for testosterone,[7] with this sanction erasing his then-world-record time of 9.77 seconds in the 100 meters.

He was eventually noticed by University of Tennessee coaches Vince Anderson and Bill Webb, who awarded him a scholarship and trained him to become a sprinter rather than a hurdler.

Gatlin appealed on the grounds that the positive test had been due to medication that he had been taking since his childhood, when he was diagnosed with attention deficit disorder.

In an unexpected move, Gatlin decided to turn professional after his sophomore season, foregoing his remaining two years of collegiate eligibility.

In his first indoor season as a professional athlete, Gatlin won the national 60 meters title in Boston in 6.45 seconds, a personal best.

On August 15, despite a very inconsistent few months, Gatlin finally broke ten seconds in the 100 meters for the first time, with 9.97 at the Weltklasse Zürich.

In order to fully recover and prepare for next year's Olympic Games in Athens, Gatlin and his coach decided to skip the 2004 indoor season.

With Crawford not entered, Gatlin won the 200 as well, becoming the second man in history to win both events at a single world championships.

[13] Shortly thereafter, with the track and field community itching for a Gatlin-Powell showdown[citation needed], the two both appeared at the Prefontaine Classic in Oregon.

On July 29, a month after winning the US title, Gatlin told the media that he had been informed by the USADA that he had given a positive doping test in April the same year.

The USADA's chief executive officer explained "Given his cooperation and the circumstances relating to Mr Gatlin's first offence, the four-year penalty issued by the arbitration panel is a fair and just outcome".

[22] On May 4, 2007, the Tampa Bay Buccaneers announced that Gatlin was one of 28 free agents taken to their 2007 rookie camp on tryout contracts, and was considered to be the most intriguing unsigned athlete in attendance.

[2] In his absence, Gatlin's teammate Tyson Gay took the 100, 200 and 4x100 meters relay titles at the 2007 World Championships in Athletics in Osaka.

His coach, Loren Seagrave, acknowledged that the sprinter's starts were poor, but that Gatlin's finish to the race remained strong.

[27] Running at the final meet of the Finnish Elite Games series in Joensuu, Gatlin won in the absence of injured Steve Mullings.

He represented the United States at the IAAF World Championships in Daegu, South Korea, where he was eliminated in the semi-finals of the 100 meters.

Outdoors, Gatlin returned to the Qatar Athletic Super Grand Prix, the same meet and venue where he broke the 100 meter world record until it was annulled.

After taking wins in Daegu, Rabat, and at the Prefontaine Classic in Eugene, Gatlin placed himself as a favorite for a medal at the 2012 London Olympics.

On August 5, 2012, at the London 2012 Summer Olympics, he recorded a new personal best time of 9.79 seconds in the 100 meters final, when he won bronze behind Usain Bolt and Yohan Blake.

On June 6, 2013, Gatlin beat world record holder Usain Bolt by one-hundredth of a second to win the 100 meters at the Golden Gala meet in Rome, Italy.

[29] On August 11, 2013, Gatlin won a silver medal behind Usain Bolt in the 100 meters at the IAAF World Championships in a time of 9.85.

This was the second fastest time of the season, behind his world lead of 19.68 that he set at the Monaco Diamond League earlier in the year.

At the USATF Track and Field Championships, Gatlin set a new personal best in the 200 meters, running 19.57 which was the fifth fastest performance in history.

On the 9th of July at the Lausanne Diamond League, Gatlin ran 9.75 once again and beat Tyson Gay and Asafa Powell by a considerable margin.

[citation needed] Before the start of his outdoor season, Gatlin ran the 100 m in 9.45 s which would be a world record but was assisted by a wind turbine.

He beat his American teammate Christian Coleman, who won the silver, and Usain Bolt (in his final World Championships) who earned the bronze.

At 37 years, 230 days, Gatlin became the oldest sprinter to win a medal in the men's 100 meters at the World Athletics Championships.

In 2021, Gatlin attempted to become the oldest man to win a medal in the 100m by qualifying for the 2020 Summer Olympics in Tokyo, Japan at the age of 39.

In April 2021, he won the Tom Jones Memorial Invitational with a time of 9.98 against a field of potential gold medal contenders.

During the final he came up with a hamstring injury and limped across the finish line in last place, ending his chances of qualifying for the Tokyo Olympics.