Belt attended Hudson High School in Hudson, Texas, where he was a pitcher and outfielder. The Boston Red Sox selected Belt in the 11th round (343rd overall) of the 2006 Major League Baseball draft as a pitcher, but chose not to offer him the signing bonus that would make him forgo his college commitment.
Belt enrolled at San Jacinto College in order to preserve his ability to negotiate with Boston, but eventually chose not to sign. He pitched and served as a designated hitter for San Jacinto's baseball team in 2007. He was drafted in the 11th round (348th overall) of the 2007 Major League Baseball draft by the Atlanta Braves, but again chose not to sign.
Belt transferred to the University of Texas, where he played college baseball for the Texas Longhorns for two years. In his 2008 sophomore season, Belt batted .319 with six home runs and a team-high 65 RBIs while also pitching in 16 games as a reliever. After the 2008 season, he played collegiate summer baseball with the Harwich Mariners of the Cape Cod Baseball League. As a junior, Belt transitioned to first base due to shoulder problems. In 2009, during his junior season, Belt batted .323 in 63 games (76-for-235) with eight home runs, 43 RBIs, and 15 stolen bases, while recording a .989 fielding percentage, as part of the Texas team that finished as runner-up in the College World Series.
The San Francisco Giants selected Belt in the fifth round (147th overall) of the 2009 Major League Baseball draft after his junior year, and he signed for a signing bonus of $200,000. He started his professional career with the High-A Giants affiliate in San Jose, for whom he was a mid-season All Star. He worked with the Giants coaching staff and made an adjustment to his swing mechanics that helped him move quickly through the Giants farm system. He hit well at all three levels in 2010 finishing the year batting .352/.455/.620 with 23 home runs and 112 RBIs and gaining attention as one of the Giants top prospects.
In 2010, he played for the San Francisco Giants Class-AAA-affiliate Fresno Grizzlies, and was named a Baseball America Minor League All Star and an MiLB Organization All Star. He also played for the East Division Scottsdale Scorpions in the Arizona Fall League, where he was named a Rising Star and to the All Prospect Team. Belt played in the Arizona Fall League Rising Stars Game for the East team.
He was ranked as the third-best first baseman prospect on MLB.com prior to the 2011 season. He was ranked as the 26th-best prospect overall by MLB.com
Brandon has now played in the Major Leagues for over 10 years. He is a two time World Series champion in 2012 and 2014. He was also an All Star in 2016
Brandon fell in love with bass fishing at the start of quarantine in 2020 when his high school baseball coach, Glen Kimble, took him fishing on Rayburn for the first time. Ever since then Brandon makes an effort to go fishing any chance he gets. He bought his first Bass Cat boat in April of 2020 and hasn’t looked back since.