Mahomes attended Whitehouse High School in Whitehouse, Texas. He played football, baseball and basketball. In football, he had 4,619 passing yards, 50 passing touchdowns, 948 rushing yards and 15 touchdowns as a senior. In baseball, he threw a no-hitter with 16 strikeouts in a game his senior year. He was named the Maxpreps Male Athlete of the Year for 2013–2014.
Mahomes was a rated by Rivals.com as a three-star football recruit and was ranked as the 12th best dual-threat quarterback in his class. He committed to Texas Tech University. Mahomes was also a top prospect for the 2014 Major League Baseball Draft, but was not expected to be selected high due to his commitment to Texas Tech. He would be selected by the Detroit Tigers in the 37th round, but would not sign.
Mahomes entered his freshman season as a backup to Davis Webb. Mahomes saw his first career action against Oklahoma State after Webb left the game with an injury, completing two of five passes for 20 yards with one touchdown and an interception. After Webb was again injured, Mahomes started his first career game against Texas. He completed 13 of 21 passes for 109 yards in the game. Mahomes would remain the starter for the final three games after that. Against Baylor, he threw for a Big 12 freshman record 598 yards with six touchdowns. For the season, he passed for 1,547 yards and 16 touchdowns with four interceptions.
Mahomes split time with the Texas Tech baseball team, where he was a relief pitcher.
Mahomes began his sophomore season at Texas Tech as the starter at quarterback. In the first game of the 2015 season, Mahomes passed for 425 yards and four touchdowns in a 59–45 win over Sam Houston State University. He followed that up with a 361-yard passing performance against UTEP, throwing for four touchdowns and rushing for two in Tech's 69-20 win over the Miners. Against TCU, Mahomes passed for 392 yards and two touchdowns in the loss, 55–52.
Prior to the start of the 2016 season, Mahomes announced that he was leaving the baseball team to focus on football for the entire offseason.
On October 22, 2016, Mahomes would set multiple NCAA, Big 12, and Texas Tech records against Oklahoma at home. Mahomes broke the NCAA FBS records for single-game total offense with 819 yards. He also tied the NCAA record for single game passing yards with 734. He fell one short of the record for most attempts at 88. Overall, the game set NCAA records for most combined yards of total offense with 1,708, combined passing yards, and total offense by two players. The 125 combined points are the second most all time involving ranked teams.
Mahomes would finish the season leading the country in yards per game (421), passing yards (5052), total offense (5312), points responsible for (318), and total touchdowns (53). For his performance, he was awarded the Sammy Baugh Trophy, given annually to the nation's top college passer, joining head coach Kliff Kingsbury, Graham Harrell, and B.J. Symons as other Red Raiders to have won the award. He was also named an Academic All-American 2nd Team by the College Sports Information Directors of America.
Mahomes announced on January 3, 2017 that he would forego his last year of college eligibility and enter the NFL Draft.Single-game yards passing: 734 (rank t-1st) (vs. Oklahoma Oct. 22, 2016)Single-game Yards total offense: 819 (rank 1st) (vs. Oklahoma Oct. 22, 2016)
Coming out of Texas Tech, Mahomes was projected as a first or second round pick by the majority of analysts and scouts. During the throwing drills at the NFL Scouting Combine, Mahomes' passes were clocked at 60 mph, tying Logan Thomas and Bryan Bennett for the fastest pass ever recorded at the NFL combine. Mahomes was ranked the second best quarterback by SI.com, the third best by ESPN, and ranked the fourth best quarterback by NFLDraftScout.com After an impressive showing at the NFL combine, representatives from 28 NFL teams were on hand to attend his pro day at Texas Tech. He became one of the fastest rising prospects during the draft process and had 18 private workouts and visits for team, which was the most for any prospect in 2017. Among the teams and coaches that he had workouts and visits with were the Arizona Cardinals head coach Bruce Arians, New Orleans Saints head coach Sean Payton, Cincinnati Bengals quarterbacks coach Bill Lazor, and coaches from the San Diego Chargers, Cleveland Browns, Chicago Bears, and Pittsburgh Steelers.
Mahomes was drafted by the Kansas City Chiefs with the 10th overall pick in the 2017 NFL Draft. The Buffalo Bills traded the 10th overall pick to the Chiefs for their first round pick, third round pick, and the Chief's first round pick in the 2018 NFL Draft. He was the first quarterback selected by the Chiefs in the first round since they selected Todd Blackledge in the 1983 NFL Draft.
His father, Pat Mahomes, is a former professional baseball pitcher who played in Major League Baseball from 1992 to 2003.
On May 12, 2017, Mahomes and three friends were allegedly robbed at gunpoint in his hometown of Tyler, Texas after getting out of their vehicle in a driveway. A car pulled up carrying two men that approached the group and one of the suspects gestured as if they had a weapon and demanded property. Authorities were able locate the vehicle and arrested two suspects named Michael Blake Pinkerton and Billy Ray Johnson and were able to recover the property. Pinkerton was charged with aggravated robbery and is being held in Smith County Jail on $50,000 bail. Johnson was charged with tampering and fabricating physical evidence with intent to impair and two counts of possession of a controlled substance and is being held in Smith County Jail on a bond of $6,000.