A professional competitor since 1980, Smith has formerly competed in kickboxing for the companies All Japan Enterprise and K-1, Pancrase, RINGS, PRIDE, Strikeforce, International Fight League and RFA.

Raised in Seattle, Washington, Smith got into martial arts at the age of 13 after watching Bruce Lee's Chinese Connection, and having had to retreat from a fight.

His first fight was on March 4, 1982 against World Kickboxing Council's Light Heavyweight Champion Tony Morelli, who defeated him by decision after the seventh round.

Maurice moved up a weight class and won the World Kickboxing Association Heavyweight Championship from Travis Everett, knocking him out via low kicks.

In the semifinals he met Dutch fighter and future K-1 legend, Ernesto Hoost, where after a hard-fought battle Smith was knocked out by left highkick in the final round, ending his tournament.

He was scheduled to face up-and-coming wrestler Masakatsu Funaki in a mixed rules fight, but his opponent got injured and was replaced with training partner Minoru Suzuki.

During the fight, Smith kept negating Suzuki's takedown attempts by employing the pro wrestling-ruled rope scapes and a rudimentary sprawl ability, knocking him out several times with strike before finishing him with a right punch at the fourth round.

He would go to lose twice to Bas Rutten, however his loss to Shamrock was more instrumental to his career, as he became friends with him and was sent to his dojo in United States, the Lion's Den, to learn proper MMA.

Throughout the fight, Maurice showed excellent use of the sprawl technique which negated the Brazilian jiu-jitsu fighter's attempts at takedowns, as well as a remarkable submission defensive whenever Silveira was able to engage him on the ground.

Smith was considered to be a massive underdog for the bout, but shocked the mixed martial arts world with a unanimous decision victory to win the UFC Heavyweight Championship.

On May 19, 2007 Maurice Smith had his first MMA bout in almost seven years when he defeated Marco Ruas by TKO in a rematch at an International Fight League show held in Chicago.

Smith returned to the Heavyweight division and lost a unanimous decision to Matt Kovacs at Cage Warrior Combat (CWC) 9 on November 2, 2013.