Floyd Joy Mayweather Jr. was born Floyd Joy Sinclair on February 24, 1977, in Grand Rapids, Michigan, into a family of boxers. His Father, Floyd Mayweather Sr., was a former welterweight contender who fought Hall of Famer Sugar Ray Leonard. His uncles Jeff and Roger Mayweather were professional boxers, with the latter—Floyd's former trainer—winning two world championships, as well as fighting Hall of Famers Julio César Chávez, Pernell Whitaker, and Kostya Tszyu. Mayweather was born with his mother's last name, but his last name would change to Mayweather shortly thereafter. He attended Ottawa Hills High School before dropping out.

Boxing has been a part of Mayweather's life since his childhood and he never seriously considered any other profession. "I think my grandmother saw my potential first," he said. "When I was young, I told her, 'I think I should get a job.' She said, 'No, just keep boxing.'" During the 1980s, Mayweather lived in the Hiram Square neighborhood of New Brunswick, New Jersey, where his mother had relatives. He later said, "When I was about eight or nine, I lived in New Jersey with my mother and we were seven deep in one bedroom and sometimes we didn't have electricity. When people see what I have now, they have no idea of where I came from and how I didn't have anything growing up."

With Mayweather's win he became lineal champion of the division; Genaro Hernández had previously beaten Azumah Nelson, whose dominance of the super-featherweight division had prompted boxing publications to give him the vacant lineal championship. The Ring stopped awarding belts to world champions in the 1990s, but began again in 2002. Nelson won his lineal status during the 1990s; therefore, The Ring's vacant title was awarded neither to him, Hernández, nor Mayweather (although Mayweather was The Ring's #1-ranked super featherweight).

Mayweather became the first 1996 U.S. Olympian to win a world title. Following his victory Mayweather's promoter Bob Arum said, "We believe in our heart of hearts that Floyd Mayweather is the successor in a line that starts with Ray Robinson, goes to Muhammad Ali, then Sugar Ray Leonard...We believe that he epitomizes that style of fighting". After capturing the title Mayweather defended it against contender Angel Manfredy with a TKO in round two, giving Manfredy his first defeat in four years.

By the end of 1998 Mayweather was ranked by The Ring as the #8-ranked pound-for-pound best boxer in the world, and became one of the youngest recipients of The Ring's Fighter of the Year award (21, the same age Sugar Ray Robinson and Muhammad Ali were when winning their first awards). In 1999, Mayweather continued his domination of the super featherweight division by defending his title three more times. The second defense of his title was against the Argentine Carlos Rios, which he won in a unanimous decision. Mayweather, fighting past the eighth round for only the third time in his career, won on the judges' scoring 120–110, 119–108, and 120–109.

Mayweather's third title defense was against Justin Juuko, which he won via knockout in the ninth round. Juuko could not beat the count of 10 by Referee Mitch Halpern, and the fight ended in Mayweather's favor 80 seconds into that (the ninth) round. His final title defense in 1999 was against Carlos Gerena, with Mayweather winning in a seventh-round Referee technical decision (RTD). Mayweather said after the fight, "I want to show the world that along with Oscar De La Hoya and Roy Jones Jr., I'm the best fighter in the world". This dominance did not go unnoticed in the boxing world; by the end of the year, the 22-year-old Mayweather was ranked The Ring's #2 pound-for-pound best boxer in the world (behind Roy Jones Jr.).

Before making the fifth successful defense of his title against former WBC Featherweight Champion Gregorio Vargas in early 2000, Mayweather fired his Father as his manager and replaced him with James Prince. A few months after the fight, the rift between Father and son grew when Mayweather also fired the elder Mayweather as his trainer. In a 2004 interview Mayweather said that although he loves his Father, he had a better chemistry with Roger because his Father had put too much pressure on him to be perfect. Mayweather, in his fifth title defense, won a near-shutout over "Goyo" Vargas in Las Vegas. During the 10th round, when Mayweather overheard HBO announcer Jim Lampley say that the champ had switched to a southpaw stance for the second time in the bout he leaned ringside and said "It was the third time". After a six-month layoff, Mayweather was still elusive. During the sixth round, Mayweather dropped Vargas with a hook to the ribs and cruised to a unanimous decision.

Mayweather commented after the fight, "Although it will take some time to make the match, I want to fight Kostya Tszyu". Tszyu, an Australian-based Russian, by then had established himself as the best light welterweight in the world. Mayweather did not get a chance to fight Tszyu, but went on to fight Ricky Hatton (who defeated Tszyu and won his Ring light welterweight championship). By the end of 2001, Mayweather was still ranked The Ring #1 super featherweight and #5 best pound-for-pound boxer in the world.

In 2002, Mayweather was charged with two counts of domestic violence and one count of misdemeanor battery. He received a six-month suspended sentence and two days of house arrest and was ordered to perform 48 hours of community Service.

In the fifth round, Mayweather connected with a series of straight rights and lefts; when N'dou would not go down, Mayweather gave a little smile and continued the barrage. He dominated his opponent, before flooring him with a series of rights in the seventh round. N'dou got up on shaky legs, forcing a stoppage at 1:50. At times during the fight, Mayweather (in black trunks outlined with fur) seemed to toy with N'dou. By the end of 2003, Mayweather was still The Ring's lightweight champion and the #5-ranked best pound-for-pound boxer in the world.

In 2004, Mayweather was given a one-year suspended jail sentence, ordered to undergo counseling for "impulse control" and pay a $1,000 fine (or perform 100 hours of community service) after being convicted of two counts of misdemeanor battery against two women.

In 2005, Mayweather pleaded no contest to a misdemeanor battery charge after hitting and kicking a bouncer, receiving a 90-day suspended jail sentence.

After his fight with Judah it was reported that Mayweather rejected an $8 million offer to fight Antonio Margarito, citing his split with promoter Bob Arum as the reason. However, Oscar De la Hoya postponed his decision until 2007, leaving Mayweather to obtain Mayweather Promotions and choose his next opponent. Mayweather considered moving up in weight again to fight light middleweight champion Cory Spinks, but because of negative publicity and Spinks' impending mandatory defense of his title, he decided to face WBC and The Ring welterweight champion Carlos Baldomir on November 4, 2006, in Las Vegas.

Mayweather appeared on the fifth season of Dancing with the Stars; his partner was Ukrainian-American professional ballroom Dancer Karina Smirnoff. On October 16, 2007, Smirnoff and Mayweather were the fourth couple to be eliminated from the competition, finishing in ninth place.

In 2008, Mayweather recorded a rap song titled "Yep" that he used for his entrance on WrestleMania XXIV in his match against Big Show.

Mayweather was guest host for Raw in Las Vegas on August 24, 2009. He interfered with a tag-team match, which resulted in a loss for the Big Show (again a heel) and his partner Chris Jericho as Mayweather gave MVP brass knuckles to knock Jericho out, giving MVP and his new tag-team partner Mark Henry the win and a shot at the Unified WWE Tag Team Titles at WWE Breaking Point against Jeri-Show. He then celebrated with Henry and MVP, turning face. Later that night, he was involved in a backstage segment with Vince McMahon, D-Generation X, and Carlito, helping McMahon prepare for his six-man tag team match against The Legacy and DX. During the segment, McMahon knocked out Carlito.

On September 9, 2010, it was reported that Mayweather was being sought by police for questioning after his former girlfriend, Josie Harris, filed a domestic battery report against him. Harris accused Mayweather of battery in the past, but those charges were dropped in July 2005 after Harris testified that she had lied and that Mayweather had not battered her. Mayweather was taken into custody September 10, 2010, but was released after posting $3,000 bail. Mayweather was initially charged with felony theft (stemming from the disappearance of Harris's mobile phone); on September 16 two felony coercion charges, one felony robbery charge, one misdemeanor domestic-battery charge and three misdemeanor harassment charges were added.

On December 21, 2011, a judge sentenced Mayweather to serve 90 days in the county jail for battery upon Harris in September 2010. Mayweather reached a deal with prosecutors in which he pleaded guilty to misdemeanor battery in exchange for prosecutors dropping the felony battery charge. Mayweather also pleaded no contest to two counts of misdemeanor harassment, stemming from threats to his children. In addition to the 90-day sentence Mayweather was ordered to complete 100 hours of community Service, a 12-month domestic-violence program and to pay a fine of $2,500. On June 1, Mayweather began serving his county jail sentence, and was released on August 3, 2012.

On June 1, 2012, Mayweather reported to the Clark County Detention Center in Las Vegas to serve his 87-day jail term for domestic abuse. After serving two months, he was released from prison on August 3, 2012. On February 4, 2015, Mayweather, who was planning to do a tour in Australia, was denied a visa on the basis of his Criminal record and jail term.

At the time of stoppage, the scorecards read 89–81, 89–82, and 87–83 all in favor of Mayweather. McGregor was praised by Dana White at the post-fight press conference for landing 111 punches of 430 thrown (26%) on Mayweather, more than what Pacquiao or any of Mayweather's previous nine opponents had landed. Mayweather was more than twice as accurate, however, landing 170 of 320 punches thrown (53%).

On July 10, 2014, Mayweather made the announcement that a rematch with Maidana (35–4, 31 KOs) was confirmed. The fight was to take place on September 13, 2014, at the MGM Grand Garden Arena, with Mayweather's WBA (Super), WBC and The Ring welterweight titles at stake, as well as Mayweather's WBC light middleweight title. The fight was billed as he fight billed as "Mayhem".

Mayweather had until 4:30 p.m. EST on July 3 to vacate the two other belts and pay a $200,000 sanctioning fee. He did not comply, and the WBO vacated the title on July 6, 2015.

Around May 2016, another rumor started that a crossover fight between Mayweather and MMA star Conor McGregor was in the works. On May 7, 2016, Mayweather confirmed that he was the one who started the rumors regarding the potential clash. Mayweather followed it through with an Instagram post of an unofficial teaser poster showcasing both fighters. Mayweather reportedly talked to Freddie Roach to train McGregor for the fight in case it would happen. Dana White dismissed all the rumors and stated that Mayweather had yet to contact him in case he wanted the fight to push through, since McGregor was in contract with the UFC. On January 13, 2017, White continued his stance against a Mayweather-McGregor boxing matchup and insisted it would never happen due to McGregor's contract and even went as far as offering Mayweather to box McGregor in the UFC for $25 million.

In May 2015, following his bout against Pacquiao, Josie Harris sued Mayweather for $20 million for defamation, claiming that Mayweather lied during an interview with Katie Couric in April. During that interview, he called her a drug abuser while discussing the 2010 domestic-violence incident which ended up with Mayweather going to jail for two months. The case remains pending as of September 19, 2017.

Mayweather said of the fight, "This was my last fight. Tonight, ladies and gentlemen, for sure I chose the right dance partner to dance with. Conor McGregor, you are a hell of a champion." He added, "He’s a tough competitor and I think we gave the fans what they wanted to see. I owed them for the Pacquiao fight. I must come straight ahead and give the fans a show, and that’s what I gave them." McGregor felt the fight was stopped prematurely, but nevertheless respected the decision and admitted he was tired. Mayweather agreed with the stoppage, and explained that he avoided inflicting more damage on McGregor to protect him from brain damage, saying "He has a career. You know, he still has a career. ...(It could've been) very damaging."