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.[2][3]
As a redshirt 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.[4][5] His 449 completions and 714 attempts were both Pac-12 and Washington State records.[6] His 4,597 yards were also a school record and his 34 touchdowns tied Ryan Leaf for most in school history.[7] In the 2013 New Mexico Bowl, he threw for 410 yards and six touchdowns in a loss against Colorado State.[8]
On October 4, during his senior season, he set the NCAAFBS passing yardage record by passing for 734 yards in a loss to Cal.[9]Texas Tech quarterback Patrick Mahomes would match this record in 2016. The previous record of 716 yards was set by Houston quarterback David Klingler in the 1990 Coca-Cola Classic. On November 1, Halliday suffered a broken tibia and fibula when his leg got caught underneath USC defensive lineman Leonard Williams, ending his college career.[10]
Halliday signed with the Washington Redskins on May 2, 2015, after going undrafted in the 2015 NFL draft.[11] He was released on May 15, 2015, after not showing up to the team's minicamp.[12] It was later confirmed that Halliday had decided to retire.[13] On October 6, 2015, he was signed to the BC Lions' practice squad. He was released by the Lions on October 8, 2015.[14] He was signed to the Montreal Alouettes' practice squad on September 30, 2016. He was released by the Alouettes on October 17, 2016.[15] Halliday signed with the Alouettes on April 17, 2017, and was released on April 19, 2017.[16] Connor decided to retire from pro football after he tore his right rotator cuff in camp with the Alouettes.[17]
^"TRANSACTIONS – 2015". cfl.ca. Archived from the original on December 31, 2016. Retrieved January 21, 2017.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
^"TRANSACTIONS – 2016". cfl.ca. Archived from the original on January 21, 2017. Retrieved January 21, 2017.{{cite web}}: CS1 maint: bot: original URL status unknown (link)