Foster began his professional MMA career in 2006, after his brother died. In an interview with FightLockdown.com, Foster stated that "martial arts have changed me, it's made me a more humble and respectful individual. My brother’s death did make me a very angry person, so very shortly after it happened, I started training and used the physical stress of training to cancel out the emotional pain caused by his death. I like to think he is very proud of what I have accomplished since his passing [...] I take a photo of my brother with me to every fight."
At UFC 106 on November 21, 2009, Foster defeated Brock Larson by TKO in the second round after taking an illegal kick to the head and an illegal knee to the head in the first round.
Foster next faced Forrest Petz on September 15, 2010 at UFC Fight Night 22. He won in the first round by TKO.
Foster defeated LaVerne Clark via first-round submission at Capital City Cage Wars 7 on October 15, 2011.
In his second fight for the promotion, Foster defeated LaRue Burley via knockout with a right hook at 34 seconds of the first round at WSOF 23 on September 18, 2015.
Foster faced Luiz Firmino at WSOF 33 on October 7, 2016. He won the fight via triangle choke submission in the first round.
Foster faced Jon Fitch in a welterweight title bout on June 30, 2017 at Professional Fighters League 36: Fitch vs. Foster. He lost the fight in the second round due to submission.
