Dix was a highly successful amateur athlete, setting a state record in the 100 m and trying out for the US Olympic Team at the age of eighteen.

He joined Florida State University and in his first year he broke the 100 m American junior record and won at the NCAA Outdoor Championships.

The son of a track and field coach, Walter Dix competed at athletics meetings from a young age, specialising in sprinting and the long jump.

At his first regional meeting for the university, he won the 60-meter dash, 200 m and 4×400 meter relay, and was chosen as the Atlantic Coast Conference rookie of the year.

[4] He made his first major impact at the NCAA Indoor Championships: after a sixth-place finish in the 60 m, he came second in the 200 m with a world junior record of 20.37 s, beaten only by Wallace Spearmon.

[1][5] Following this, he became USA Track & Field's Athlete of the Week after setting an American junior record in the 100 m. Running in the Icahn Stadium at the 2005 NCAA East Regional Championships, his heat-winning time of 10.06 seconds bettered Stanley Floyd's 25-year-old mark.

[8] He completed a 200 m NCAA Championship double by taking the outdoor title, and he also finished as runner-up in the 100 m, second to Xavier Carter.

[13] At the NCAA Outdoor Championships that year, he won three separate national titles, beating all opposition in the 100 m, 200 m, and 4×100 meter relay races.

[15] However, he returned in April to win his third 200 m NCAA outdoor title, while placing fourth in the 100 m. Although his personal bests rivalled those of top professional athletes, Dix decided to finish his degree in social science at FSU, as his graduation in May 2008 allowed him to focus on the Olympic Trials thereafter.

[21] In the final he registered a personal best of 9.91 seconds, finishing behind new world record holder Usain Bolt of Jamaica and Richard Thompson of Trinidad and Tobago.

[22] A few days later, he finished fifth in the 200 m final with a time of 19.98 seconds, some distance off the winner Usain Bolt who had broken the world record.

However, it transpired that both the silver and bronze medalists (Churandy Martina of the Netherlands Antilles and American Wallace Spearmon) had stepped out of their lanes thus they were disqualified.

[20] He placed third behind Michael Rodgers and Asafa Powell at the Prefontaine Classic but, unusually, this proved to one of the highlights of a low-profile year for Dix.

[31] With his father as his coach, a legal battle and no major races to prepare for, Dix ran only a handful of local meetings in the rest of 2009.

In the first meeting of the 2011 IAAF Diamond League, at the Qatar Athletic Super Grand Prix, he won the 200 m with a time of 20.06 seconds.

[40] He achieved a 100/200 sprint double at the 2011 USA Track and Field Championships, winning in the absence of Tyson Gay and Wallace Spearmon.

[41] Running in both the events at the 2011 World Championships in Athletics, he first secured the silver medal in the 100 m final – defending champion Bolt was disqualified for a false start and Dix was runner-up to another Jamaican, Yohan Blake, in a comparatively slow 10.08 seconds.

Blake was even faster (19.26), however, leaving Dix in second place even as he became the fourth fastest 200 m runner of all-time and then won the league series.

[45] He moved to Southern Ireland in 2012 to train with John Smith and opened his outdoor season with a wind-aided run of 9.85 seconds.