A professional competitor since 2002, he has formerly competed for World Victory Road, BAMMA, and was the winner of The Ultimate Fighter: Brazil 2 welterweight tournament.

[6] Santos make his MMA debut against rising undefeated Japanese superstar Takanori Gomi, who at the time was the Shooto World Welterweight (154 lb) Champion.

[7] After this bout Santos returned to BJJ full-time, winning the CBJJO World Cup Championship 4 times between 2002 and 2005.

In 2006 after a short time helping his brother Wagnney with his academy in Canada, Leonardo started dedicating himself fully to MMA.

[10] He won his elimination fight to get into the TUF house, defeating Luciano Contini by TKO in round 1.

However, Ponzinibbio broke his hand during this semifinal fight and was replaced by Santos in the finals against William Macário.

Santos faced returning veteran Efrain Escudero on September 13, 2014, at UFC Fight Night 51.

[15] However, Wiman was forced out of the bout on February 11 with a back injury and was replaced by Anthony Rocco Martin.

[17] Despite being a significant underdog, Santos won the fight via TKO in the first round and earned a Performance of the Night bonus.

[20] However, Santos pulled out on April 29 due to an undisclosed injury and was replaced by James Vick.

[35] Santos was scheduled to face Alexander Hernandez on October 2, 2021, at UFC Fight Night 193.