Manziel was born in Tyler, Texas, on December 6, 1992, to Michelle (nee Liberato) and Paul Manziel. He has a younger sister named Meri. Manziel's great-great-grandfather Joseph immigrated to the United States in 1883 from the Mount Lebanon region of Syria in what is now Lebanon. He is of Italian descent on his maternal side.

Texas A&M faced uncertainty at the quarterback position when Ryan Tannehill left for the National Football League after the 2011 season. Manziel performed well during spring ball and fall practices and won the starting job over Jameill Showers and Matt Joeckel before the season began. His first game was supposed to be against Louisiana Tech in Shreveport, Louisiana on Thursday, August 30, 2012, but the game was postponed until October 13 due to Hurricane Isaac hitting the Louisiana coast two days prior to game time. Consequently, Manziel's college football debut was played as a redshirt freshman against the Florida Gators before a home crowd at Kyle Field.  Although Manziel began the season in relative obscurity, his play against Arkansas in which he broke Archie Manning's 43-year-old total offense record gained him some attention. Manziel produced 557 yards of total offense, breaking Manning's record of 540. Two games later, Manziel surpassed his own total offense record against #24 Louisiana Tech by achieving 576 yards of total offense, becoming the first player in SEC history to have two 500+ total offense games in one season. After Texas A&M's blowout of Auburn in the eighth game of the season, in which Manziel accounted for 3 passing and 2 rushing touchdowns through only the first half plus one series in the second, Manziel began showing up in national Heisman Watch lists.  Manziel was launched into the national scene after he led Texas A&M to a 29-24 victory over #1 Alabama in Tuscaloosa. In that game, Manziel accounted for 345 of A&M's 418 yards of offense, including two passing touchdowns. In the following days, Manziel became the frontrunner for the Heisman Trophy in most national watch lists and polls due to his performance during the game combined with other Heisman frontrunners faltering.  On November 24, during the game against the Missouri Tigers before a home crowd, Manziel left the game with an apparent knee injury late in the first quarter. He returned to the field for the next series of downs wearing a knee brace and finished the game with 439 yards of total offense, including 3 passing and 2 rushing touchdowns. During the game, he broke the single season record for offensive production in the SEC with 4,600 yards, surpassing Cam Newton and Tim Tebow, notable recent Heisman Trophy winners. He also became the first freshman and only the fifth player in NCAA history to pass for 3000 and rush for 1,000 yards in a season, reaching that mark two games earlier than any other player. He won the SEC Freshman of the Year Award and College Football Performance National Freshman of the Year Award. Manziel won the Davey O'Brien Award on December 6 and the Heisman Trophy on December 8, making him the first freshman ever to win either award.

Did he break any records in the year 2012?
He also became the first freshman and only the fifth player in NCAA history to pass for 3000 and rush for 1,000 yards in a season,