Many of the regular cast members on The Flash / Supergirl already had extensive experience performing in Broadway and West End (London) musicals before this musical episode. Jesse L. Martin played Tom Collins in the original cast of RENT, as well as in the 2005 movie version of the musical. Victor Garber (Martin Stein) was in the original Broadway cast of Sweeney Todd, and he played Jesus in the 1973 movie of the musical Godspell; two of his four Tony nominations are for musical performances. John Barrowman (Malcolm Merlyn) has been in Sunset Boulevard and Putting it Together on Broadway and is an even bigger star on London's West End, where he has performed in such musicals as Anything Goes, Phantom of the Opera, Hair, and Miss Saigon. Jeremy Jordan (Winn Schott) was in the original Broadway casts of Rock of Ages, Bonnie and Clyde, and Newsies: The Musical, for which he was nominated for a Tony Award in 2012. Tom Cavanagh (Wells) was in the Broadway musicals Urinetown and Shenandoah. Grant Gustin (Barry Allen / The Flash) appeared in the 2010 Broadway revival of West Side Story. "Legends of Tomorrow" actor Arthur Darvill played the lead role in the musical"Once" on Broadway and in the West End and has written and composed musicals for the Globe Theater.
Carlos Valdes (Cisco Ramon) and
Darren Criss (The Music Meister) attended the University of Michigan together; they worked together within the theatrical group StarKid Productions.
