Stating that he was "in love with improv and comedy"[6] he began improvisation lessons[7] and participated in stage productions at the Roxy Performing Arts Center.

[8] Eager to pursue a career in acting, Jenner left Miami and moved to Los Angeles after graduating from high school a year early, with just $2,500.

[3][9] While residing in California, he took on many jobs including a waiter, clothing store associate, and parrot salesman while auditioning for acting roles.

[15] Jenner, along with co-stars Jacob Artist, Becca Tobin, Alex Newell, and Melissa Benoist, was promoted to series regular status for the fifth season.

[17] In late 2015, Jenner was cast in a recurring role as Adam Foster on Supergirl, playing opposite his then-wife Melissa Benoist, who stars as the series' title character.

Jenner played Christian de Neuvillette in the Goodspeed Musical production's Cyrano at the Norma Terris Theatre in August and September 2018.

[24] In August 2019, it was announced that Jenner would star in Richard Linklater's film adaptation of Merrily We Roll Along, which would be shot over the course of twenty years.

[33][34] Benoist also stated she had experienced extreme control, manipulation, and cycles of severe violence including being slapped, punched, shoved into a wall, dragged by her hair, and choked during the relationship.

[35] In October 2020, Jenner responded via an Instagram post in which he admitted to causing the eye injury and confirmed the infliction of abuse throughout the relationship.