Memphis Grizzlies (2008–2012) On June 26, 2008, Mayo was selected 3rd overall in the
2008 NBA draft by the
Timberwolves. Later that day, he was traded, along with
Marko Jarić,
Antoine Walker, and
Greg Buckner, to the
Memphis Grizzlies in exchange for
Kevin Love,
Mike Miller,
Brian Cardinal, and
Jason Collins. Mayo was a part of the
Select Team that helped get the
U.S. national team ready for the
2008 Summer Olympics in Beijing. Mayo was the runner-up for the 2008–09
NBA Rookie of the Year Award, finishing second behind
Chicago Bulls point guard
Derrick Rose. On November 1, 2009, Mayo scored a career-high 40 points against the Denver Nuggets on 17 of 25 shooting. Mayo was late for a game-day shootaround and was taken out of the starting lineup starting November 20, 2010. On a return flight to Memphis from Los Angeles, Mayo was involved in a fight with teammate
Tony Allen over a debt from an in-flight card game. On January 27, the NBA suspended Mayo for 10 games following a positive test for the steroid
dehydroepiandrosterone (DHEA), which violates the league's anti-drug program. Mayo blamed an over the counter supplement that he didn't know was banned by the NBA for the positive test, but he declined to say which supplement he used.
Dallas Mavericks (2012–2013) The Grizzlies did not sign a qualifying offer sheet for Mayo, making him an
unrestricted free agent. On July 19, Mayo officially signed with the Mavericks. On December 8, Mayo tied his career-high of 40 points in a game against the
Houston Rockets. Two days later, he tied a career high of playing 52 minutes in a double-overtime loss to the Boston Celtics. On December 28, 2012, Mayo had a career high of 5 steals against the
Denver Nuggets. On March 6, Mayo recorded a new career high of 12 assists against the
Houston Rockets. After Nowitzki, the Mavericks' all-time leading scorer, returned, Mayo saw his scoring average dip. Mayo said, "I'm a scorer and can shoot the ball a little bit, but I like to be a playmaker. I like to try to take what the defense gives you and not just concentrate on scoring the ball. Find other guys." Mayo finished the season with averages of 15.3 points, 4.4 assists and 3.5 rebounds while playing a team-high 35.5 minutes per game. His production dropped considerably after the
All-Star break, when star player Nowitzki re-emerged after missing the first 27 games. On April 18, 2013, he announced he would decline the player option on his contract for the following season and become a free agent.
Milwaukee Bucks (2013–2016) On July 13, 2013, Mayo signed a three-year, $24 million contract with the
Milwaukee Bucks. The signing was essentially a trade of starting shooting guards, as
Monta Ellis departed Milwaukee to sign with Dallas. On October 30, 2013, in his Bucks debut, Mayo recorded 13 points and 5 rebounds in a loss to the
New York Knicks. Mayo later missed time during the 2013–14 season due to issues with his conditioning as he appeared in a career-low 52 games. Mayo bounced back for the Bucks in 2014–15, recording seven 20-plus point games on the season. In Game 4 of the Bucks' first round playoff match-up against the
Chicago Bulls, Mayo scored 18 points and hit a clutch three-pointer with 1:42 left in the game to give the Bucks a six-point lead. On November 19, 2015, Mayo made his season debut for the Bucks after missing the first 11 games of the season due to a strained right hamstring he suffered in the final preseason game. On December 5, he had a season-best game after coach Jason Kidd started him at point guard, largely due to the Bucks being down on point guards due to injury. In 35 minutes of action, he recorded 17 points and 5 assists in a 106–91 win over the New York Knicks. On February 9, 2016, he returned to action against the Boston Celtics after missing 11 games with a left hamstring injury. On March 10, he was ruled out for the rest of the season after he suffered a fractured right ankle. On July 1, 2016, Mayo was dismissed from the NBA for a drug violation. He was eligible for reinstatement around the start of the
2018–19 NBA season.
Atléticos de San Germán (2018) On April 4, 2018, Mayo was reported to sign with
Atléticos de San Germán of the
Baloncesto Superior Nacional. On June 27, he was released. Mayo started 18 of his 21 appearances with the team, shooting just 39.0 percent from the field and 34.7 percent from beyond the arc. He averaged 13.4 points, 3.9 rebounds, 3.5 assists and 1.1 steals.
Dacin Tigers (2018–2019) On October 22, 2018, Mayo was reported to sign with
Dacin Tigers of the
Super Basketball League in Taiwan. Mayo finished the 2018–19 SBL season with averages of 22.7 points, 7.3 rebounds, 4.3 assists and 1.6 steals in 36 total games played (33 in the regular season and 3 in the playoffs), averaging 28.2 minutes per game and shooting 47.7% from the field (36.2% from the 3-point line).
Hunan Jinjian Rice Industry (2019) Soon after the Taiwan's SBL season ended, Mayo signed with
Hunan Jinjian Rice Industry of
National Basketball League (NBL), the second-tier league in China.
Taipei Fubon Braves (2019–2020) On October 17, 2019, the
Taipei Fubon Braves officially announced that they signed Mayo for the upcoming
ASEAN Basketball League (ABL) season.
Liaoning Flying Leopards (2020–2021) Mayo signed with the
Liaoning Flying Leopards of the
Chinese Basketball Association (CBA) and made his debut in the
2019–20 CBA season on June 23, 2020, scoring 28 points in a 102–106 loss to the
Guangzhou Loong Lions. On July 17, 2020, Mayo scored 44 points in a win against
Ty Lawson's
Fujian Sturgeons, while shooting 8–10 from the three-point line. On July 26, Mayo won the CBA Player of the Month award for the month of July. Over 15 regular season games, Mayo averaged 28.4 points, 7.1 rebounds, 4.3 assists and 2.5 steals per game, shooting 57% from the field (43.5% from three) in 35.9 minutes of average playing time. On November 13, 2020, Mayo set a new career-high of 48 points in a win against the
Qingdao Eagles. He also had 8 rebounds and 6 assists.
UNICS (2021–2022) On September 20, 2021, Mayo signed a one-year contract with the Russian team
UNICS Kazan of the
VTB United League. On February 7, 2022, Mayo scored a buzzer-beating game-winner against arch-rivals
CSKA Moscow to give UNICS the win after triple overtime. He averaged 7.2 points on 35.4% shooting in nine games.
Zamalek (2022–2023) In December 2022, Mayo joined the Egyptian club
Zamalek of the
Egyptian Basketball Super League. == National team career ==