Kimbrel attended Wallace State Community College. While at Wallace State in 2007, Kimbrel had an 8–0 win-loss record with a 1.99 earned run average (ERA) as a freshman in 2007, serving as the team’s closer and a spot starter. In 2008, he was 9–3 with a 2.88 ERA, striking out 123 hitters in 81 innings pitched, mainly as a reliever.

Kimbrel got his first call-up from the Gwinnett Braves on May 15, 2010, to replace the injured Jair Jurrjens on the roster. He was called up for the second time in his career on June 4, 2010, to replace Takashi Saito, who was placed on the 15-day DL. He earned his first major league save on September 19, 2010 against the New York Mets. Kimbrel’s record for the 2010 season was 4–0, with one save and a 0.44 ERA in 20 ⁄3 innings. He recorded 40 strikeouts and 16 walks. In the 2010 NLDS, he was the losing pitcher in Game 3 against the eventual World Series Champion San Francisco Giants.

Kimbrel made the roster to start the 2011 season as the team’s primary closer. He was successful in his first four save opportunities before blowing his first career save on April 21, 2011. On June 3, 2011 in a game versus the New York Mets, Kimbrel passed the record for most saves by a National League rookie before the All-Star break. He is the fastest Braves pitcher to reach 100 career strikeouts, doing so in 59 ⁄3 career innings. His new record surpassed the previous record set by John Rocker in the 1998–1999 season, where it took Rocker 70 career innings to reach the 100 career strikeout mark. On July 5, his 26th save matched Jonathan Papelbon’s record for most saves by a rookie before the All-Star break. On July 7, Kimbrel’s 27th save of the year against the Colorado Rockies broke Papelbon’s record.

On July 22, 2011 in a game versus the Cincinnati Reds, Kimbrel broke the Braves rookie record for saves in a season (31).

On August 9, 2011 in a game versus the Florida Marlins, Kimbrel tied the National League rookie record for saves in a season (36 by Todd Worrell of the St. Louis Cardinals in 1986). He broke that record on August 17 in a game versus the San Francisco Giants. On August 21, 2011, Kimbrel recorded his 100th strike out which coincided with his 39th save of the season and a string of 30 ⁄3 innings without yielding a run. On August 23, 2011, Kimbrel recorded his 40th save, tying the rookie save record of Neftalí Feliz. He subsequently broke this record with his 41st save on August 31 with two strikeouts in a game against the Washington Nationals. At the time, he led the majors in saves and had not given up a run in his last 34 innings. The following night, Kimbrel surpassed Cliff Lee’s mark of 34 scoreless innings with 34 ⁄3 scoreless innings for the longest scoreless streak in the majors in 2011. He was named the NL Rookie of the Month and MLB Delivery Man of the Month for August 2011. His scoreless inning streak came to an end after 38 ⁄3 innings, on September 9, 2011.

Kimbrel’s four-seam fastball was the 12th-fastest among Major League relievers in the 2011 season. In addition, he threw the hardest curveball, averaging 87 mph. His fastball had the fifth-highest whiff rate among relief pitchers (32%), and he also had the highest whiff rate of any reliever’s curveball, at better than 55%. His pre-pitch stance has also been widely noted and has been dubbed “Kimbreling”, or “How to Destroy Your Back by 35”, or “Spider Arms”.

Kimbrel again made the All-Star team in 2012. He struck out the two batters he faced. He won the MLB Delivery Man Award for September 2012. On September 26, he struck out four batters in the ninth inning.

Kimbrel was thoroughly dominant throughout the 2012 season. He led the National League with 42 saves (in 45 opportunities) and Win Probability Added among pitchers. He struck out 116 batters in 62 ⁄3 innings, producing a K/9 rate of 16.7. In so doing, he also became the first pitcher in history to strike out at least half the batters he faced during a season. He also went to an 0–2 count on 56% of the batters he faced. Kimbrel allowed only 3.9 hits and 2.0 walks per 9 innings he pitched, giving him a WHIP of 0.65 and a batting average against of .126. He finished with an ERA of 1.01. He won the NL Rolaids Relief Man Award. Kimbrel finished fifth in the 2012 National League Cy Young Award voting, and eighth in the 2012 National League MVP voting.

He married former Wallace State cheerleader Ashley Holt in 2012. The couple’s first child, a daughter named Lydia Joy, was born on November 3, 2017. She was born with heart defects and has undergone two surgeries thus far.

Kimbrel began the 2013 season with three blown saves during his first nine save opportunities, tying his personal record for blown saves during the entire 2012 season. Nonetheless, on May 9, 2013 in a game against the San Francisco Giants, Kimbrel earned his 100th save making him the second youngest player in MLB history to reach that mark. With a save against the Cardinals on July 27, 2013, he became only the second Atlanta pitcher after John Smoltz to have three 30-save seasons. Kimbrel surpassed John Smoltz’s Braves record of 27 consecutive saves on August 17, 2013.

Kimbrel was named the closer for Team USA in the 2013 World Baseball Classic. Despite not surrendering one lead off double all year with the Braves in 2012, Kimbrel gave one up to Nelson Cruz of the Dominican Republic in their round two matchup. Kimbrel would go on to give up two runs in the game, and be the losing pitcher in Team USA’s 3–1 loss to the eventual champions.

On February 16, 2014, Kimbrel agreed to a four-year, $42 million extension with the Braves that ran through 2017, with an option for 2018. On April 2, Kimbrel tied Gene Garber’s 141 saves with the Braves, good for second in franchise history. Two days later, April 4, Kimbrel recorded his 142nd career save, to move into sole possession of second place. On April 25, 2014, Kimbrel became the fastest pitcher ever to reach 400 strikeouts—reaching the mark in 236 innings’ worth of work. On June 6, 2014, Kimbrel recorded his 155th save in a game against the Arizona Diamondbacks, surpassing John Smoltz as the new franchise leader in saves. On August 29, 2014, Kimbrel recorded his 40th save of the season. He became the third pitcher to reach that single-season milestone in four straight seasons.

On April 5, 2015, Kimbrel was traded to the San Diego Padres along with outfielder Melvin Upton, Jr., in exchange for Carlos Quentin, Cameron Maybin, prospects Matt Wisler, Jordan Paroubeck, and the 41st overall pick in the 2015 MLB draft.

On November 13, 2015, the Padres traded Kimbrel to the Boston Red Sox in exchange for Manuel Margot, Javy Guerra, Carlos Asuaje, and Logan Allen.

On July 8, 2016, Kimbrel injured his knee while taking warmups. The next day, an MRI revealed that there was a tear in the medial meniscus of the left knee. The injury required surgery, and three to six weeks to recover. He returned to the bullpen at the start of August.

For the 2016 Red Sox, Kimbrel made 57 regular season appearances, finishing 47 games while recording 31 saves. In 53 innings pitched, he had a 3.40 ERA while striking out 83 and walking 30.

In the 2016 American League Division Series, Kimbrel made two appearances; he retired all four batters he faced, three by strikeout, as the Red Sox were swept by the Cleveland Indians.

On May 11, 2017 against the Milwaukee Brewers at Miller Park, Kimbrel struck out the side in the ninth inning on nine consecutive pitches, joining Pedro Martínez and Clay Buchholz as the only pitchers in franchise history to accomplish this feat, commonly referred to as an immaculate inning. Two weeks later, Kimbrel recorded a second four-strikeout inning while facing the Texas Rangers.

For the 2017 Red Sox, Kimbrel made 67 regular season appearances, finishing 51 games while recording 35 saves. In 69 innings pitched, he had a 1.43 ERA while striking out 126 and walking 14. Of all MLB pitchers, he held right-handed batters to the lowest batting average, .108 (in 30 or more innings).

In the 2017 American League Division Series, Kimbrel made two one-inning appearances; he faced a total of 12 batters, giving up four hits, one walk, and one run while recording two strikeouts, as the Red Sox lost to the eventual World Series champions, the Houston Astros.

On May 5, 2018, facing the Texas Rangers, Kimbrel recorded his 300th career save. He achieved this milestone in fewer games (494), fewer save opportunities (330), and at a younger age (29) than any other pitcher. On July 8, Kimbrel recorded his 27th save of the season, and was named to the 2018 MLB All-Star Game. For the 2018 regular season, Kimbrel recorded 42 saves in 63 appearances, pitching to a 2.74 ERA with 96 strikeouts in 62 ⁄3 innings.

On June 7, 2019, Kimbrel signed with the Chicago Cubs on a three-year contract, reportedly worth $43 million. On June 27, he was added to the Cubs’ major league roster from the Triple-A Iowa Cubs, and recorded his first save of the season, against Atlanta. On August 5, 2019, he was placed on IL for a knee inflammation. On August 18, 2019, he was reactivated from the IL to help the Cubs beleaguered bullpen. He finished the year 0-4 with 13 saves and a 6.53 ERA in 23 games.