A well rounded Brazilian competitor, Alex "Cowboy" Oliveira worked as a construction worker and was also a bullrider before transitioning to muay thai. He trained in muay thai for a few years before switching to mixed martial arts at the age of 22.

 
Fighting out of the Tata Fight Team in Três Rios, he made his professional debut on December 10, 2011, with a knockout over local competitor Rodrigo Pitbull. He compiled a professional record of 10-1-1 (1), including a two-fight stint for Bitetti Combat, and after winning a unanimous decision over Joilton Santos, Oliveira signed with the UFC in 2015.

His first fight in the UFC saw him face off against rising welterweight prospect Gilbert Burns. With the massive amount of hype surrounding Burns, few expected the fight to go down as it did, with Oliveira successfully utilizing his long reach to keep the jiu-jitsu expert at bay for two rounds, punishing him with jabs and hooks and defending Burns' takedowns well. In the third round of a fight that the Brazilian Cowboy had been winning easily, Burns heeded to his corners advice and finally got the fight down to the floor, where he and Oliveira took turns making transitions on the canvas, before he finally tapped out Oliveira with a slick armbar.

Oliveira rebounded from the tough loss with impressive wins over K.J. Noons, Joey "Slash" Merritt, and a Performance of the Night bonus winning knockout over Piotr Hallmann. In his last fight on February 21, 2016, Brazilian Cowboy lost by triangle choke in a short notice fight against former title challenger and contender Donald "Cowboy" Cerrone in the main event of UFC Fight Night 83.

He will face welterweight prospect James Moontasri on July 23, 2016, at UFC on Fox 20.