Mangum was born in Flowood, Mississippi and grew up in nearby Pearl, Mississippi and attended Jackson Preparatory School. While playing for the Patriots Mangum was a member of three consecutive state championship teams in baseball and was named a Louisville Slugger All-American in 2013 and 2015 and Perfect Game All-American in 2013, 2014 and 2015 and Mississippi Association of Independent Schools first team All-State in 2014 and 2015. As a senior, Mangum was named the MIAS AAA, Division I Player of the Year after hitting.504 with 46 runs scored and 41 RBIs and compiling an 8-0 record with four saves, 66 strikeouts, and a 1.48 ERA in 52 innings pitched. Mangum originally committed to play college baseball at the University of Alabama, his father's alma mater, over offers from Ole Miss and Auburn. However, he ultimately de-committed from Alabama and instead chose to play for Mississippi State.
College career
As a freshman, Mangum led the Southeastern Conference and finished 7th in the NCAA with a.408 batting average along with 84 hits, one home run, 40 runs scored and 28 RBIs. He was named the SEC Freshman of the Year and first team All-SEC, as well as Freshman All-America by the National Collegiate Baseball Writers Association and Baseball America. Mangum was also named second team All-America by the NCBWA, third team All-America by the American Baseball Coaches Association, and was the first freshman to be awarded the C Spire Ferriss Trophy as the top collegiate baseball player in the State of Mississippi. As a sophomore, Mangum slashed.324/.380/.385 in 65 games with 90 hits, 51 runs scored, 26 RBIs and 14 stolen bases and was named second team All-SEC. In addition to playing in the outfield, Mangum also pitched for the Bulldogs and posted a 2-1 record with a 6.46 ERA in six appearances and a save in his only relief appearance. Despite breaking his left hand sliding into third base in early April in a game against Kentucky, Mangum continued to play the rest of the season although he could not bat right handed and his batting average fell dramatically. Mangum was selected in the 30th round of the 2017 Major League Baseball draft by the New York Yankees following the season but opted to return to Mississippi State for his junior year. During the summer he played for the Bourne Braves of the Cape Cod Baseball League, batting.300 with nine RBIs and 11 stolen bases in 35 games and was named to the Cape Cod All-Star team. In his junior season, Mangum led the SEC with 101 hits and 22 doubles in an NCAA-leading 288 at bats while hitting.351. He was named first team All-SEC and to the SEC All-Defensive team and Rawlings Division I Gold Glove Team as the Bulldogs advanced to the 2018 College World Series, making it to the semifinals before losing to eventual champion Oregon State. He was selected with the 950th pick in the 32nd round of the 2018 MLB Draft by the New York Mets but again decided to return to school, reportedly turning down a $300,000 signing bonus. Following the season he played a second summer in the Cape Cod League with the Hyannis Harbor Hawks and was named to the All-Star team for a second straight year. On April 26, 2019 Mangum passed Eddy Furniss as the all-time hits leaders in SEC history with his 353rd career hit. He set the MSU single season hit record with 108 in his final career game against Louisville in the College World Series. He was again named first team All-SEC and was awarded the Ferriss Trophy, becoming the first player to receive it twice. He was also named third team All-America by Collegiate Baseball Newspaper, becoming the second player in program history to be named an All-American in three different seasons after Rafael Palmeiro. Mangum finished his collegiate career with a school and conference record 383 hits and at bats with 1,074, as well as school records for games played and doubles and finished second with 229 runs, third with 507 total bases, fourth with 56 stolen bases and tied for the 10th-highest career batting average at.357. Mangum was selected by the Mets again in the 2019 MLB Draft in the fourth round. Following the Bulldogs loss to Louisville in the College World Series, Mangum made an impassioned appeal for the NCAA to allow programs to pay a third coach and to raise the scholarship limit beyond the current allowance of 11.7, revealing that he chose to give up his scholarship and play as a walk-on for his final two seasons so that Mississippi State could use the scholarship money elsewhere.
Professional career
Mangum signed with the Mets on June 24, 2019 for a signing bonus $20,000 which was well below the slated bonus amount of $487,900 for his slot. He was assigned to the Brooklyn Cyclones of the Class A Short SeasonNew York–Penn League to begin his professional career. In his first professional season, Mangum batted.247 with 45 hits, 29 runs scored, 18 RBI and a team-leading 17 stolen bases in 53 games.
