Yorkey was born in Omaha, Nebraska, where he was raised, before his family moved to Issaquah, Washington. He graduated from Columbia University where he served as the Artistic Director of the Varsity Show. He is an alumnus of the BMI Lehman Engel Musical Theater Workshop.
Prior to bringing Next to Normal to Broadway, Yorkey was affiliated with Village Theatre in Issaquah, where he began as a KidStage student and eventually progressed to a seven-year tenure as Associate Artistic Director. Four musicals written by Yorkey—Funny Pages (1993), Making Tracks (2002), The Wedding Banquet (2003), and Play it by Heart (2005)—were staged there.
While at Village Theatre, Yorkey founded the KidStage Company class which teaches teens to write, direct, and perform their own musicals. Yorkey's frequent collaborator, Tom Kitt, joined him in assisting with the score to the 2008 Company Original, In Your Eyes. He worked with composer Tim Symons, on other Company Originals such as Last Exit and A Perfect Fall.
During Yorkey's tenure as Village Theatre's Associate Artistic Director, he developed a comprehensive new works program, Village Originals. The Village Originals program develops approximately ten new musicals each season, in various stages from reading to full production. Yorkey is credited with the development of over 50 new musicals, including the 2010 Broadway musical, Million Dollar Quartet, which was nominated for Best Musical, Best Book of a Musical, and won Best Performance by a Featured Actor (Levi Kreis) in a Musical at the 64th Tony Awards.