[5] At HBHS, he attended the district magnet program, the Huntington Beach Academy for the Performing Arts, as a Musical Theater major and played the lead Don Lockwood in Singin' in the Rain.
[9][11] In August 2013, while still attending Carnegie Mellon University, Selig was cast as the standby for the lead role of Elder Kevin Price in the Broadway production of The Book of Mormon.
[24] For seven weeks in early 2016, he led the Broadway company of The Book of Mormon as Elder Price, replacing Gavin Creel, who left the production to star in She Loves Me.
[27] In the summer of 2016, he appeared as Baby John in West Side Story at the Hollywood Bowl with the Los Angeles Philharmonic, alongside Jeremy Jordan and Karen Olivo.
[29][30] In the spring of 2017, Selig portrayed Dauphin in The Public Theater's world premiere of the off-Broadway rock musical, Joan of Arc: Into the Fire directed by Alex Timbers.
[36] In December 2019, it was announced that Selig would be taking a leave of absence from Mean Girls, and internet personality and actor, Cameron Dallas, would be filling the role of Aaron Samuels for four-week engagement.
[40] It was announced on August 15, 2024 that Selig would return to Broadway in Water for Elephants, replacing Grant Gustin in the starring role of Jacob Jankowski beginning September 3, 2024 until the show closed on December 8.
[42] In August 2018, Selig participated in Covenant House's Stage & Screen Sleep Out along with Mean Girls co-stars Ashley Park and Curtis Holland, and together they raised over $14,000 for this organization which provides shelter, food, and crisis care for homeless and runaway youth.