[1] Christian was awarded a wildcard into the 2012 US Open to play doubles alongside Ryan Harrison, where they reached the quarterfinals.

Harrison won his first ATP World Tour match against Alejandro Falla at the BB&T Atlanta Open.

Harrison reached the final round of qualifying at the 2016 US Open after beating Luke Saville and second seed Konstantin Kravchuk in two three-set matches.

He also reached his maiden ATP final in doubles with his brother Ryan Harrison where they lost to Ariel Behar and Gonzalo Escobar.

[7] Harrison won his 11th Challenger title in Winnipeg with Cannon Kingsley and fourth of the season,[8] and reached the top 100 in the doubles rankings on 15 July 2024.

[10][11] Alongside Evan King, he won his first ATP Tour doubles title at the Dallas Open, defeating Ariel Behar and Robert Galloway in the final.

He has since served as a substitute for the Orange County Breakers in 2018 and the San Diego Aviators during the 2020 WTT season played at The Greenbrier.