After going undrafted in the 2010 NBA draft, Fortson signed with Steaua Turabo Bucuresti of Romania but later left in January 2011. In March 2011, he joined the Reno Bighorns of the NBA D-League. In November 2011, Fortson was acquired by the Los Angeles D-Fenders. But on December 8, 2011, he was signed by the Los Angeles Clippers. However, he was later waived before the start of the 2011–12 season and re-joined the D-Fenders. Not long after being waived by the Clippers, he was called up on January 16, 2012 on a ten-day contract. However, he was waived by the team on January 27, 2012, after playing four games. Fortson signed a ten-day contract with the Houston Rockets later that season, and was eventually signed by the Rockets for the remainder of the season. In September 2012, he was waived by the Rockets. Fortson, again, signed with the Los Angeles Clippers for training camp on September 29, 2012, but on October 7, 2012, he and Chris Johnson were waived by the Clippers. Later that month, he joined the Los Angeles D-Fenders. On February 4, 2013, Fortson was named to the Futures All-Star roster for the 2013 NBA D-League All-Star Game. In September 2013, he signed with Avtodor Saratov of Russia for the 2013–14 season. On June 3, 2014, he signed with Trotamundos de Carabobo for the rest of the 2014 LPB season. On July 5, 2014, he returned to Avtodor Saratov, signing for one more season. On February 18, 2015, Fortson scored a triple double in a EuroChallenge-game against Güssing Knights; he recorded 30 points, 12 rebounds and 13 assists and was named Weekly MVP. On July 11, 2015, Fortson signed with the Turkish club Banvit. On March 9, 2016, he parted ways with Banvit after averaging 16.2 points, 4.3 rebounds and 6.5 assists per game in BSL. In July 2016, Forston signed with Chinese club Zhejiang Lions for the 2016–17 CBA season. On January 4, 2017, Fortson recorded a triple-double after posting 22 points, 11 rebounds and a career-high 20 assists in a 117-130 loss to the Shandong Golden Stars. Fortson was named the CBA MVP for the 2017–18 season, after he averaged 31.1 points, 12 assists and 7.8 rebounds per game while leading Zhejiang to the first seed in the CBA.
