Stevenson's known name is an inversion of his family name and given name.
Born in Port-au-Prince, Haiti, Stevenson moved to Montreal, Quebec with his family when he was seven. By 14 years old, he was living on the streets and soon fell into a violent gang which drew him into a criminal lifestyle. In his early twenties, after a criminal trial in 1998 in Quebec, Stevenson served 18 months of a four-year prison sentence for managing prostitutes, assault, and issuing threats. While in prison, he also pleaded guilty to aggravated assault after putting a fellow inmate into a coma. After leaving prison in 2001, Stevenson vowed he would never return.
Stevenson became Quebec Middleweight champion in 2004, and best amateur fighter of the country in 2005–2006. He also grabbed the Canada national title in 2005 and 2006. Stevenson competed in the XVIII Commonwealth Games in Melbourne, Australia in 2006 and won the silver medal losing to local Australian Jarrod Fletcher in the final. It was also the only medal a Canadian boxer received at the games.
He holds a record of 33–5 in amateur contests.
A 29-year-old Stevenson turned professional in September 2006. His opponent was Mike Funk, another boxer making his debut, at the Montreal Casino in Montreal, Quebec, Canada. Stevenson knocked Funk out with a hook in twenty-two seconds.
On August 1, 2009, at Windsor Station in Montreal, Quebec, Canada, Stevenson defeated Anthony Bonsante by first round knockout. The two fighters came out of their corners for the fight with Bonsante launching the first attack, but just moments after the assault, Stevenson landed a left hand that sent Bonsante down to the canvas. Bonsante sprawled out on the canvas with his eyes closed, while the referee reached the count of six before stopping the fight. Bonsante had begun to get up at the count of six, but it was too late, leaving Bonsante livid with the decision as he chased the referee around the ring in an attempt to protest the decision, but to little avail. He also won a fifth-round TKO decision against Jermain Mackey on September 25, 2009.
On April 17, 2010, in his first fight in the United States, which also was his first time fighting for promoter Lou DiBella, he suffered his first defeat being stopped in the second round by Darnell Boone. Boone had been knocked down on the canvas twice in the first round, however, in the second round, Stevenson rushed to Boone without maintaining his defense and he got caught by a solid right sending him on the canvas for the first time in his career. Stevenson managed to get back on his feet inside the count of 10, however, the referee waved the fight off as he deemed Stevenson unable to continue.
Nonetheless, Stevenson resumed with GYM Promotions and won the North American title NABA on April 8, 2011 at the expense of Derek Edwards by KO in the third round. He then won by referee stoppage in the first round against Dion Savage (Shujaa El-Amin) on September 17, 2011, and retained his title against Aaron Pryor Jr on December 10, 2011 by referee stoppage in the ninth round. Stevenson jumped from 15th to 2nd position for the IBF title, winning by KO in the first round duel against Jesús González on February 18, 2012. He then fought Noe Gonzalez on April 20, 2012 and won the fight at 1:40 in the second round when the referee stopped the fight.
His next fight originally set to be against Don George with the winner getting a shot at the IBF champion. The fight was originally scheduled to be a co-main event of a fight card also including a match between Jean Pascal and Tavoris Cloud on August 11, 2012 but the even was cancelled due to an injury suffered by Pascal. The Stevenson fight was then moved up to August 17, 2012 and was set to be part of ESPN Friday Night Fights, but Stevenson later injured his hand cancelling the fight. The fight was then rescheduled to October 12. In the fight Stevenson knocked George down twice in the fifth and once in the sixth round before winning the fight with a 12th-round TKO after knocking him down twice more.
Stevenson avenged his only loss, knocking out Darnell Boone with a pair of lefts in the sixth round in March 22, 2013 at the Bell Centre. The left-hander, fighting at 171.9 pounds, forced Boone to take a knee with a right hook to the body early in the sixth, then stunned him coming out of a corner with a left uppercut, followed with a straight left that sent Boone on the canvas.
Stevenson moved up to light heavyweight to face Lineal/WBC/The Ring champion Chad Dawson (31-2, 17 KOs) on June 8, 2013. Stevenson hit Dawson with a left hook that dropped him very early in the first round of the fight, and although Dawson got up before the count of eight the referee stopped the fight giving Stevenson an unexpected knockout victory. Stevenson's victory was his eighth straight since his only career defeat, all coming by knockout. At 174 1/4 lbs., Stevenson was fighting at the heaviest weight of his professional career to date. The knockout was voted as Ring Magazine Knockout of the Year for 2013.
The WBC originally ordered Stevenson to face mandatory challenger Tony Bellew, but then allowed him to make a voluntary defense first against Tavoris Cloud, where the winner of the fight must face Bellew at a later date.
On September 28, Stevenson fought Tavoris Cloud (24-1, 19 KOs) and dominated the precedings, flustering Cloud with quick hands and shocking power. The result ended when Cloud failed to answer the bell for the start of the eighth round.
On November 30, 2013, Stevenson defended his light heavyweight title against Tony Bellew (20-1-1, 12 KOs) at the Colisée Pepsi. Stevenson became the first boxer to stop Bellew winning the fight via TKO. In round 6, Stevenson put Bellew down with a left hand, he beat the count and the referee let the fight go on. Bellew was then knocked out standing by another pair of left hands before the referee could get in and put a stop to the bout. At the time of stoppage, Stevenson was ahead on the scorecards 50-45, 49-46, 50-45. Bellew contemplated moving up to cruiserweight after the loss. According to Nielsen Media Research firm, the fight attracted an average of 1.3 million viewers on the HBO network, making it the 5th most watched bout of 2013.
Stevenson defended his lineal/WBC/The Ring titles against 26 year old Andrzej Fonfara (25-2, 15 KOs) on May 24, 2014, in Montreal, Quebec. Stevenson started off very well, dropping his opponent twice with sharp lefts and appeared close to stopping his opponent. Fonfara however, recovered very well, even dropping Stevenson in the ninth round. Stevenson similarly recovered quickly. The two fighters exchanged punches in a good-action final round and the crowd gave the fight a standing ovation. Stevenson won the fight as the judges scored it 116-109, 115-110 & 115-110. In the post-fight interview, Stevenson claimed he hurt his left hand in the second round. He added that he was willing to fight Bernard Hopkins or Sergey Kovalev next, but would leave the decision to his manager, Al Haymon.
On December 19, 2014 Stevenson defended his belts against Russian contender Dmitry Sukhotsky (22-2, 16 KOs) in Quebec City, Quebec. This was his fourth defense of his titles. Stevenson retained his belts via a fifth round stoppage following a one punch knockout. Stevenson was in control from the opening bell, throwing minimal punches as the crowd started to boo. In round 2, he managed to floor Sukhotsky with a left hand.
Stevenson faced 35 year old contender Sakio Bika (32-6-3, 21 KOs) on April 4, 2015. The judges scored the fight (115–110, 116–110, 115–110).
Stevenson later faced Tommy Karpency (25-4-1, 14 KOs) on September 11, 2015. Karpency, previously coming off the biggest win of his career, a split decision win against former light heavyweight champion Chad Dawson, the man who Stevenson beat to win the light heavyweight championship. Karpency was thought to be a stepping stone for Adonis, and he was. After barely escaping round 2, Karpency got knocked down at the beginning of round 3. He immediately knocked Karpency down after he got up, and the referee called a halt to the bout, awarding Adonis a TKO victory in round 3.
In November 2015, citing the fact that Stevenson hadn't faced a top-ranked opponent in the last two years, The Ring Magazine stripped Stevenson of his belt.
On May 31, 2016, it was announced that Stevenson would defend his WBC and Lineal titles against 28 year old southpaw Thomas Williams Jr. (20-1, 14 KOs) on July 16 in Quebec headlining a Premier Boxing Champions card. This was Stevenson's seventh defense of his WBC and Lineal light heavyweight titles. Williams weighed in the heaviest of the two at 174.6lbs with Stevenson in at 173.6lbs. In a brief slug fest, Stevenson knocked out Williams in round 4 to retain his titles in his seventh successful defense. Stevenson connected with a hard left to Williams' head in round one that floored him with approximately 30 seconds left, however Williams beat the referees count.
Undefeated Colombian boxer Eleider Álvarez (22-0, 11 KOs) became mandatory challenger following his win over Isaac Chilemba in November 2015. He then knocked out former super-middleweight world champion Lucian Bute in February 2017 in a final eliminator to become mandatory challenger once again for the WBC light heavyweight title. On February 27, 2017 the WBC ordered negotiations to begin between Stevenson and Álvarez, who are both managed by Al Haymon and promoted by Yvon Michel of GYM for a deal to be reached within 30 days or they would force a purse bid on March 24. Stevenson had a return date scheduled for April 29 at the newly renovated Nassau Coliseum in New York. Promoter Yvon Michel, stated on behalf of Álvarez, that he had averted from his mandatory position to allow Stevenson a voluntary defence.
On April 8, Stevenson revealed on social media that he had finalized a deal to fight Andrzej Fonfara (29-4, 17 KOs) in a rematch from their first fight in 2014. Yvon Michel later told ESPN that the fight would take place in Canada, at the Centre Bell in Montreal Quebec on June 3, 2017. The last time Stevenson fought at that arena was in 2014 against Fonfara. Michel didn't go into detail around why a fight with Seanie Monaghan, who he was tipped to fight originally in New York, never materialized, but said, if he continues winning, the fight could still happen. Fonfara started the fight well in round 1, connecting with the jab. Stevenson, who was patient with his left hand, eventually landed a left hook to the head of Fonfara, dropping him to the canvas. Fonfara beat the count, but was on steady legs and when he got backed up to in the corner, the bell saved him from an onslaught. Round 2 opened with Stevenson carrying on where he left of, pummeling Fonfara with huge lefts. The fight came to an abrupt end, when Fonfara's trainer, Virgil Hunter stepped up on the apron after just 28 seconds, motioning to the referee to stop the bout, which referee Michael Griffin did. Stevenson retained his WBC and Lineal world titles. When asked who Stevenson would fight next, he replied, “I’m the greatest at 175. I don’t have to call out anybody,” On the same card, Eleider Álvarez defeated Jean Pascal via majority decision to remain mandatory to Stevenson.
After Badou Jack (21-1-3, 13 KOs) defeated Nathan Cleverly in August 2017, to win the WBA 'Regular' light heavyweight title, he began to call out Stevenson, knowing that Stevenson had a mandatory challenger. Stevenson shrugged it off, claiming he was ready for anyone, "It was a good performance. He beat Cleverly now. So now he called me out and I'm ready. I'm ready to fight and I'm ready to unify the title. For Andre Ward or him, I'm ready. It doesn't matter to me [which one]. It's great for me to unify and add another title to my collection. I want to unify the titles. This is my goal and that's what I want to do," On September 8, 2017 mutual promoter Yvon Michel disclosed that there was serious ongoing negotiations between Stevenson and mandatory challenger Eleider Álvarez (23-0, 11 KOs) to fight before the end on 2017. He revealed the fight would take place in Quebec.
In 2012, in response to questioning at a press conference before a fight, Stevenson admitted to serving jail time in Bordeaux, Quebec on charges of managing prostitutes, assault, and making threats. Stevenson served four years in prison for these crimes and crimes that took place while in prison, and was released in 2001.