Lottomatica Roma (2008–2009) On July 16, 2008, Jennings signed with
Lottomatica Roma of the Italian
Serie A. The contract he signed with Roma was for $1.65 million
net income guaranteed. After earning the contract with Lottomatica,
Under Armour gave Jennings a $2 million contract to showcase their products in the
Euroleague. Jennings was the first American player to go straight from high school to play professionally for a European team rather than play for a
college basketball team since the NBA's age restriction rule was implemented. In the Serie A 2008–09 season, Jennings averaged 5.5 points in 17.0 minutes per game over 27 games. He shot 35.1% from the field and 20.7% from 3-point range. In 16
Euroleague games, Jennings averaged 7.6 points in 19.6 minutes per game, shooting 38.7% from the field and 26.8% from 3-point range.
Milwaukee Bucks (2009–2013) Jennings was selected tenth overall by the
Milwaukee Bucks in the
2009 NBA draft, becoming the first player who skipped college to play professional basketball in Europe to be drafted by an NBA team. He made his NBA regular season debut on October 30, 2009, against the
Philadelphia 76ers. He nearly recorded a
triple double, scoring 17 points and recording 9 rebounds and 9 assists in 34 minutes. On November 14, 2009, in just his seventh game in the NBA, after being held scoreless in the first quarter, Jennings scored 55 points in a win over the
Golden State Warriors. Jennings's 55 points broke the team record for most points in a game by a rookie, previously set by
Kareem Abdul-Jabbar in 1970, and was more than any rookie scored since
Earl Monroe scored 56 in 1968. He became the youngest player to ever score 55, collecting the second-highest total for a player under 21, behind only
LeBron James's 56 points in March 2005, and the second-most points scored by a Milwaukee Buck (behind
Michael Redd's 57 in 2006). His 55-point tally was also the highest for any NBA player in a 2009–10 regular season contest. During
All-Star Weekend, he competed in the
Skills Challenge. Jennings started all 82 games as a rookie and led the Bucks to the playoffs for the first time in four seasons, where they lost to the
Atlanta Hawks in seven games. He finished third in
Rookie of the Year voting. On October 30, 2010, Jennings recorded his first ever triple double with 20 points, 10 rebounds, and 10 assists in a win against the
Charlotte Bobcats. On December 15, 2010, Jennings broke his left foot against the
San Antonio Spurs when he came down awkwardly on his ankle. Despite the injury, he finished the game and played 30 minutes the following game against the
Utah Jazz. The team later confirmed that Jennings would miss the next four to six weeks as he recovered from surgery to repair a fracture in his left foot. Jennings missed a total of 19 games with the injury. He scored a season-high 37 points against the
New York Knicks at
Madison Square Garden on March 25, 2011. With Milwaukee struggling in Jennings's absence and his slow return to form after the injury, the
Bucks missed the playoffs. With the NBA beginning the 2011–12 season in a
lockout, Jennings played in the
Drew League to stay in shape and prepare for the season. With the schedule shortened after the lockout ended, Jennings played and started in all of the 66 games. He recorded career highs with 19.1 points and 1.6 steals in 35.3 minutes per game. Similar to the previous season, his season high in points came in Madison Square Garden against the Knicks; this time, Jennings scored 36 points in a 100–86 win. The
Bucks again missed the NBA playoffs, finishing in ninth place in the East. With Jennings set to hit restricted free agency at the end of the 2012–13 season, he sought a long-term contract, saying he would not return to Milwaukee if they did not work out an agreement. During the Bucks' home opener against the
Cleveland Cavaliers, Jennings made a game-winning three at the buzzer to win the game for the Bucks. Jennings teamed up with
Monta Ellis, who was acquired at the 2012 trade deadline, to form one of the NBA's most potent backcourts that year. With improved play under new coach
Jim Boylan,
Milwaukee returned to the playoffs for the first time since Jennings was a rookie, qualifying as the eighth seed. They were swept 4–0 by the reigning champions, the
Miami Heat, who would go on to win the
NBA Finals again. After the team lost Game 2, Jennings proclaimed the Bucks would win the series in six. The phrase "Bucks in 6" subsequently became a famous phrase among the fanbase, commonly used during the
2021 NBA Playoffs when the
Bucks won the
NBA Finals, coincidentally in six games after trailing 2–0. Jennings was subsequently invited to participate in the team's championship parade and helped design their championship rings.
Detroit Pistons (2013–2016) On July 31, 2013, Jennings was
signed-and-traded to the
Detroit Pistons in exchange for
Brandon Knight,
Khris Middleton and
Viacheslav Kravtsov. He agreed to a three-year contract, reportedly worth $25 million. On December 5, 2013, Jennings returned to Milwaukee in a 105–98 win over the Bucks, finishing with 17 points and 11 assists. On January 11, 2014, in a game against the
Phoenix Suns, Jennings recorded 16 assists in the first half, tying
Isiah Thomas' franchise record for the most assists in a half. On January 16, 2015, Jennings scored a season-high 37 points on 10-of-23 shooting in the 98–96 win over the Indiana Pacers. Five days later, he recorded 24 points and a career-high 21 assists in the 128–118 win over the Orlando Magic, becoming the first player to record a 20-point, 20-assist game in the NBA since
Steve Nash in
2009. On January 25, 2015, Jennings was ruled out for the rest of the season due to a ruptured left Achilles tendon that required surgery. On the season, he averaged 15.4 points, 6.6 assists and 1.1 steals in 41 games. On December 17, 2015, Jennings voluntarily reported to the
Grand Rapids Drive, the Pistons'
D-League affiliate, on a rehab assignment. In his debut with the Drive on December 19, Jennings recorded a
double-double with 11 points and 12 assists in 27 minutes against the
Iowa Energy. He was recalled by the Pistons the next day. On December 29, Jennings made his first appearance of the season for the Pistons, scoring seven points and adding four assists in 16 minutes off the bench against the New York Knicks. He had a season-best game in his fourth game back from injury, recording 17 points and 6 assists off the bench on January 4 in a 115–89 win over the Orlando Magic.
Orlando Magic (2016) On February 16, 2016, Jennings was traded to the
Orlando Magic, along with
Ersan İlyasova, in exchange for
Tobias Harris. The next day, he made his debut with the Magic in a 110–104 win over the
Dallas Mavericks, recording 18 points, three rebounds and four assists in 25 minutes.
New York Knicks (2016–2017) On July 8, 2016, Jennings signed with the
New York Knicks. He debuted in the Knicks's season opener on October 25, 2016, against the
Cleveland Cavaliers. In 21 minutes off the bench, he recorded seven points, three rebounds and five assists in a 117–88 loss. On December 11, he scored 15 of his season high-tying 19 points in the fourth quarter of the Knicks' 118–112 win over the
Los Angeles Lakers. On December 31, he set a new season high with 32 points in a 129–122 loss to the
Houston Rockets. On February 27, 2017, he was waived by the Knicks. He had previously requested a trade due to lack of playing time and team success in New York.
Washington Wizards (2017) On March 1, 2017, Jennings signed with the
Washington Wizards. That year the Wizards won the division for the first time in 38 years, losing to Boston in seven games in the Eastern Conference semi-finals.
Shanxi Brave Dragons (2017) On July 28, 2017, Jennings accepted a one-year, $1.5 million deal to play for the
Shanxi Brave Dragons of the
Chinese Basketball Association. On December 9, 2017, he was released by Shanxi. In 13 games, he averaged 27.8 points, 5.1 rebounds, 6.8 assists and 2.7 steals per game.
Wisconsin Herd (2018) On February 13, 2018, Jennings was acquired by the
Wisconsin Herd of the
NBA G League.
Return to Milwaukee (2018) On March 11, 2018, Jennings signed a 10-day contract with the
Milwaukee Bucks, returning to the franchise for a second stint. The following day, in his first game back with the Bucks, Jennings finished two rebounds shy of a triple-double with 16 points and 12 assists in a 121–103 win over the
Memphis Grizzlies. He signed a second 10-day contract on March 21, and a multi-year contract on April 1. On August 1, 2018, he was waived by the Bucks.
Zenit Saint Petersburg (2018) On August 20, 2018, Jennings signed a one-year deal with the Russian team
Zenit Saint Petersburg of the
VTB United League. His contract with Zenit was terminated on November 20, 2018, after only 10 games and days after an Instagram post he made stating "Lesson in life: I will never play for a team and the dad is coaching his SON! Never again!" The father-son duo at the club at the time of his Instagram post were
Vasily Karasev (then head coach of Zenit Saint Petersburg) and former NBA player
Sergey Karasev. ==Career statistics==