Kelly has also gained publicity for his comical repertoire, such as skillfully dancing in the outfield during practice, disguising himself while interviewing the unwitting rapper Nelly , and engaging in lengthy staredown with Los Angeles Dodgers outfielder Scott Van Slyke before a 2013 National League Championship Series game.
Early life and amateur career
Following high school Kelly attended the University of California, Riverside (UCR), and played college baseball for the Highlanders team.  An outfielder in high school, he converted to pitcher for the Highlanders and served as the closer .  He was named Big West Conference Pitcher of the Year in 2007 as a freshman.  In 2009, Kelly posted a 5.65 earned run average (ERA) with a 1–1 won–lost record (W–L record). Kelly set a Highlanders record with 24 career saves and was named an All-American . His final career stats at UCR included a 4.65 ERA and an 8–11 record in 42 career games. 
Draft and minor leagues (2009–12)
The St. Louis Cardinals drafted Kelly in the third round of the 2009 MLB draft and signed him on June 15 for $341,000. His first professional start was with the Batavia Muckdogs of the New York–Penn League , where he appeared in 16 games, posted a 4.75 ERA, pitched 30 1 ⁄ 2 innings (IP) and struck out 20 (SO). 
The Cardinals began to use Kelly as a starting pitcher with the Quad Cities River Bandits to get him more innings and develop his secondary pitches. He succeeded in the role and remained a starter.  For the season, Kelly appeared in 26 games on the mound, made 18 starts, pitched 103 1 ⁄ 3 innings, registered 92 SO, 103 hits allowed (H) and 45 walks (BB) for a 4.62 ERA and 6–8 record. 
In 2011, Kelly advanced from the high-A level to AA, pitching for the Palm Beach Cardinals of the Florida State League and the Springfield Cardinals of the Texas League . In hIs combined final seasons statistics, Kelly started 22 games, pitched 132 innings, posted 113 SO with a 3.68 ERA. The next season in AAA at Memphis he posted a 2.68 ERA in 12 starts and earned a call-up to the major league club. 
St. Louis Cardinals (2012–2014)
Kelly made his major league debut on June 10, 2012 ,  replacing the injured Jaime García in the Cardinals' starting rotation. Once García returned to the rotation, Kelly moved to a bullpen role; however, he impressed team officials so much they considered keeping him in the rotation and moving Lance Lynn to the bullpen. 
Kelly acquired his first major league hit and run batted in (RBI) as the result of a communication error. In a June 25 contest against the Miami Marlins , manager Mike Matheny attempted a double switch with the score tied 6–6 in the bottom of the ninth at Marlins Park . Matheny presented his decision to place relief pitcher Víctor Marte in the game to home plate umpire Bob Davidson in exchange for third baseman David Freese , originally batting in the seventh spot, and, at the same time, bring in Tyler Greene for the ninth position – previously assigned to the pitcher who was Marte's predecessor – to play second base . The second baseman already in the game, Daniel Descalso , would move to third base.  After Matheny presented Davidson the lineup card, he wrote "5" (used to designate the third baseman) next to Descalso's name. When Davidson conveyed the change to Marlins manager Ozzie Guillén , an error in communication occurred, because, after Marte faced one batter, Guillén emerged from the dugout to argue that Marte and Allen Craig , the number five hitter , "couldn't be on the field at the same time." Rather than countering Guillén's protest, Matheny removed Craig and substituted Tony Cruz at first base, erasing two of the Cardinals' top hitters, Craig and Freese, from the game. 
In the top of the tenth, Marte was due in Craig's fifth spot. Now having retained no regular batters, Matheny chose a speedy former college outfielder to bat for Marte, rookie pitcher Joe Kelly. The Cardinals had gained the lead, 7–6, at this point and Kelly batted with the bases loaded and two outs. He beat a ground ball for an infield hit that scored a run – his first major league hit and RBI – and put the Cardinals up 8–6. This run proved to be crucial insurance as Miami's Omar Infante scored on a John Buck single in the bottom of the tenth. Nevertheless, Jason Motte , Marte's replacement, closed it out for the 8–7 win.   
After spring training in 2013 , Kelly lost his rotation spot to rookie Shelby Miller and was relegated to the bullpen for much of the first half of the season, seeing little use.  However, he became known somewhat as a "stopper" after being reinserted into the rotation to increase its effectiveness. In August, Kelly went 5–0 with a 2.08 ERA.  He allowed an 83.3% baserunners strand rate as a reliever in and 82% as a starter and finished with a 2.69 ERA in 124 IP in 2013. In three starts against the Pittsburgh Pirates – of whom the Cardinals finished three games ahead – Kelly won all three starts.  He won ten of 15 games started in the 2013 regular season, posting a 2.69 ERA. 
Against the Milwaukee Brewers on September 22, Kelly showcased some of his speed he utilized as a former center fielder when Brewer Carlos Gómez was caught in a rundown between third base and home plate . Himself a speedy center fielder with 37 stolen bases at the time, Gómez was attempting to run back to third base when Kelly took the throw and sprinted from behind him. He caught up with Gómez, dove, and tagged him out just steps away from the bag. 
On October 6, Kelly made his first postseason start against the Pirates in the 2013 National League Division Series , which he got a no-decision. He had the same result in Game 1 of the NLCS , but lost to the Los Angeles Dodgers in Game 5. However, in Game 6, Kelly and Dodgers outfielder Scott Van Slyke created a stir before the first pitch by engaging in a lengthy staredown. Both men remained on the field after the conclusion of the United States national anthem , " The Star-Spangled Banner ," long after the rest of their teammates departed the field to await the start of the game. They maintained their positions with hats over their chests through the ground crew's preparation of the field and starting pitcher Michael Wacha 's warmup pitches. A total of about 15 minutes transpired before an annoyed Greg Gibson , the home plate umpire, scattered them. Both claimed "victory", as Kelly had smiled first, and Van Slyke had first moved from his position. 
This event induced noticeable laughter from teammates, curiosity from announcers calling the game and Twitter participants in a state of mirth. Van Slyke commented that he had "never done that. I stayed out there after the anthem was over and noticed Kelly was out there, too, and I figured I would stay longer than him. Then I caught his eye and he had this big smile, like he was telling me he could stay longer than I could, and before you know it, it was just the two of us." Kelly added, "After every national anthem, I usually stand there and wait for the other team to leave. It's something that I like doing, and I guess I feel like I get a little grin out of that. But I guess [Van Slyke] caught onto it, and he just started standing there." 
The Cardinals won the game behind Wacha's strong performance, and thus the series. Joe Kelly made his first World Series start in Game 3 against the Boston Red Sox . He received a no-decision, but the Cardinals won the game. However, they lost the series in six games, 4-2.
Joe Kelly won his 2014 debut on April 5 after the Cardinals defeated the Pirates , 6–1, despite allowing 10 base runners in 5 1 ⁄ 3 innings. He also doubled off opposing starter Francisco Liriano for his first hit of the season.  He spent most of the first half on the Disabled List, but rehabbed in Triple-A Memphis and was activated to face the Milwaukee Brewers on July 11.
He gave up six earned runs in his return from the DL, but got a no-decision when Matt Holliday , Jhonny Peralta , Kolten Wong , and Matt Adams all homered to give the Cardinals a comeback win. His next start, on July 19 against the Dodgers, was a dominant 7-inning performance that tied his longest career outing.
Boston Red Sox (2014–present)
On July 31, 2014, Kelly was traded to the Boston Red Sox along with first baseman/outfielder Allen Craig for starting pitcher John Lackey and Corey Littrell .  In 10 starts for Boston, Kelly went 4–2 with a 4.11 ERA and allowed 32 walks in 61 1 ⁄ 3 innings. In January, 2015, Kelly made a guarantee to the Boston media that he would win the A.L. Cy Young award the following season.  He began the 2015 season on the disabled list. Through his first 15 starts, he suffered through his worst season in the majors, going 2–6 with a 5.74 ERA. He had led all major league pitchers with four errors through July 27. However, in an August resurgence, he won all six starts, including August 29, a 3–1 win over the New York Mets , making him the first Red Sox pitcher since Pedro Martínez to record six wins in one month. He lowered his ERA to 4.94 in August. Kelly was shut down after September 15 due to injury. He finished the season 10–6 in 25 starts for the season.
The Red Sox placed Kelly on the DL with a right shoulder impingement on April 20, 2016 . In his return on May 21, he took a no-hitter through 6 2 ⁄ 3 IP against the Cleveland Indians until Juan Uribe broke it up with a double. Boston won, 9–1.  By the end of the 2016 season, after spending time in the minor leagues, Kelly had returned to the Red Sox roster as a reliever .  In this new role he pitched 3 2 ⁄ 3 scoreless inning in the 2016 ALDS .  He ended the 2016 season with a 5.18 ERA 
Joe Kelly throws a lively fastball that can reach up to 102.2 miles per hour  (MPH) and complements it with a sinking fastball and slider . His sinker is among the prized pitches in the game – it shows dramatic horizontal movement, while paradoxically, not showing the kind of vertical movement (sink or drop) of other sinkerballers such as former teammate Justin Masterson – and is one of the fastest in the game, at about 93 MPH. He also throws a changeup to left-handed batters and an infrequent curveball . His control of his pitches – including his fastball – receives compliments.  
- Minor leagues
- Florida State League All-Star, mid-season, 2011 
- The Cardinal Nation / Scout.com Top Prospect 2011 #27 
- Midwest League Pitcher of the Week: July 26 – August 2, 2010 
- The Cardinal Nation/Scout.com Top Cardinals Prospect 2010: #32 
- Big West Conference Pitcher of the Year, 2009 
- Preseason All-American Third Team, 2009 
- Big West Conference Pitcher of the Year, 2007 
Joe Kelly married Ashley Parks, daughter of former Minnesota Twins catcher Derek Parks , in November 2013. Kelly shared a condominium, for a time, with Shelby Miller , who he competed for a rotation spot with during the spring training of 13'.  Kelly met his wife while attending UCR.  Kelly also has a son named Knox.
Kelly has showcased his jocular side on occasions besides the 2013 NLCS. While rapper Nelly , a self-professed Cardinals fan and "unofficial mayor " of St. Louis , interviewed with Fox Sports Midwest ' s Jim Hayes before a game in 2013 featuring his bobblehead giveaway, Hayes welcomed "an older member of the Cardinals organization" to participate. This older member was Kelly wearing a mask of a bald, elderly man. Nelly never guessed that it was a prank until Kelly revealed himself after the interview. 
His mother, Andrea, is of Mexican American descent.  Earlier in the 2013 season, Kelly was spotted dancing salsa in the outfield. He attributed this urge to dance salsa to moves his mother taught him after urging him to take lessons when he was a child.  he currently resides in Rancho Cucamonga, California.