RJ Mitte began training with Los Angeles talent manager Addison K. Witt in Sherman Oaks, California, and though many of the actors in the studio were working actors, Mitte was using acting as a means to build friendship with kids his own age while living in a new city. At the encouragement of Witt and talent agent Debra Manners of the Daniel Hoff Agency, Mitte began auditioning for commercials and TV shows like Grey's Anatomy (2005). Mitte tried his hand at background roles and became a regular student on the popular Disney show Hannah Montana (2006).

Mitte was cast as Walt White Jr., a series regular, and character with cerebral palsy on AMC Network's Breaking Bad (2008). And though Mitte has a mild case of the same condition, he had to do what all actors do: research the character and even relearn many of the challenges he had endured as a child in order to convey a more pronounced version of CP. The Daily Advertiser, a Lafayette, La., newspaper learned of Mitte's work in Hollywood and featured him in an article, noting that R.J. was homegrown, and off to a great start in Hollywood.