He was raised in Overland Park, Kansas, where he attended Shawnee Mission South High School from which he graduated in 1994, having been part of the drama club.

[9][10] He described growing up in the Kansas City metropolitan area as "very traditional in one sense, and a conservative community that also had a rad, fringe, artistic, progressive tribe of people who were finding connectivity through the arts and the culture of KC and the surrounding suburbs.

He wrote about his experiences in his screenplay, Animals,[10] and continues to advocate for mental health and substance abuse treatment programs.

[2] He has received acclaim for lead roles in Tennessee Williams's The Glass Menagerie and Sam Shepard's Buried Child at Chicago's Shattered Globe Theatre.

[22] His feature film debut came in the late 2000s, as the Joker's deranged henchman, Thomas Schiff, in Christopher Nolan's The Dark Knight.

Richard Corliss of Time called Dastmalchian's performance "excellent – chatty, modest with some subtle telltale psychopathy" and The Guardian's Paul MacInnes likened his introduction as a new suspect to Kevin Spacey's entrance in Seven.

Ashley Moreno of The Austin Chronicle credits Dastmalchian's screenplay with "present[ing] an authenticity often lacking in films about drug abuse.

"[25] Film Threat's Brian Tallerico similarly sings the praises of Dastmalchian's breakout performance, noting his ability to "capture that sense of self-loathing that comes through in the body language of an addict without overselling it.

[29] In 2021, he portrayed Polka-Dot Man in The Suicide Squad,[30] a character with whom he said he connected on a personal level due to the childhood bullying he suffered as a result of his vitiligo.