Halliday was redshirted in 2010. As a redshirt freshman in 2011, Halliday appeared in four games and made one start. In the game against Arizona State he passed for a Pac-12 and Washington State freshman record, 494 yards with four touchdowns. As a refshirt sophomore in 2012, he appeared in nine games with five starts. He finished the year completing 152 of 291 passes for 1,878 yards, 15 touchdowns and 13 interceptions. As a junior in 2013, he started all 13 games. He set or tied numerous Washington State, Pac-12 and NCAA records during the season. In the game against Oregon, he broke Drew Brees' record for pass attempts in a game with 89. His 449 completions and 714 attempts were both Pac-12 and Washington State records. His 4,597 yards were also a school record and his 34 touchdowns tied Ryan Leaf for most in school history. In the 2013 New Mexico Bowl, he threw for 410 yards and six touchdowns in a loss against Colorado State.