As a freshman at Wisconsin in 2015, Hornibrook was redshirted and did not play.[7]
The following season started with Hornibrook as a backup to senior quarterback Bart Houston.[8] After playing two games as a reserve, Hornibrook earned his first start against Michigan State Spartans.[9] Throughout the season, his playing and leadership skills were at points inconsistent.[2] Although he started the rest of the games, he split playing time with Houston and eventually injured his head against Minnesota on November 26.[10] After his injury, Hornibrook was replaced by Houston.[11] He was eventually cleared to play in the 2017 Cotton Bowl Classic.[12]
The March after the 2016 season, Hornibrook met with renowned quarterbacks coach George Whitlock Jr. in San Diego.[9] In June, he attended the Manning Passing Academy.[2] Another focus during the offseason was nutrition, as Hornibrook increased his lean body mass while decreasing his body fat.[13] He was named the Badgers starting quarterback for the 2017 season.[8] Inconsistent non-conference play cast scattered doubts on Hornibrook's ability early in the season,[14] but still performed at a serviceable level.[15] Late in the season, Hornibrook quieted doubts about interception problems in a 31–0 win against Minnesota.[16] In the 2017 Orange Bowl against the Miami Hurricanes, Hornibrook was named the game's MVP after throwing four touchdowns[17] completing 23 of 34 pass attempts, finishing off a 13–1 season.[18] Hornibrook finished his Wisconsin career with the best winning percentage by any starting QB in program history he went 26-6 as the starting QB with a winning percentage of 81.3%.
On February 27, 2019, Alex Hornibrook announced he was leaving Wisconsin football's program [19]
On March 10, 2019, Hornibrook announced his intention to transfer to Florida State as a graduate transfer and was immediately eligible under the NCAA graduate transfer rules.
Hornibrook's relatives have played collegiate athletics or professionally in football, baseball, water polo, basketball, swimming and lacrosse.[3] His brother, Jake, was an offensive lineman for Stanford, his sister, Mackenzie, was a captain of the Penn State swimming and diving team, his father, Jeff, was an offensive lineman for the Temple Owls, his mother, Dawn, played basketball at Gettysburg College, his uncle, Ben Davis, was the second overall pick in the 1995 MLB Draft and had an eight-year long MLB career, his aunt, Megan Davis, played both soccer and lacrosse at Rutgers, and his great uncle, John, played quarterback for the Miami Hurricanes.[1] He was an honor roll student in high school.[4]