Joseph Mantello (born December 27, 1962) is an American actor and director known for his work on stage and screen. He first gained prominence for his Broadway acting debut in the original production of Tony Kushner's two-part epic play Angels in America (1993–1994), for which he received a Tony Award for Best Featured Actor in a Play nomination. He has since acted in acclaimed Broadway revivals of Larry Kramer's The Normal Heart (2011) and Tennessee Williams' The Glass Menagerie (2017).

Mantello has transitioned into a career as a Broadway director, winning the Tony Award for Best Direction of a Play for Take Me Out (2003) and the Tony Award for Best Direction of a Musical for Assassins (2004). He has directed notable productions such as Wicked (2003), Glengarry Glen Ross (2005), The Humans (2016), Three Tall Women (2018), and The Boys in the Band (2018).

Mantello was born in Rockford, Illinois, the son of Judy and Richard Mantello, an accountant. His father is of Italian ancestry and his mother is of half Italian descent. He was raised Catholic.

Mantello studied at the North Carolina School of the Arts; he started the Edge Theater in New York City with actress Mary-Louise Parker and writer Peter Hedges. He is a founding member of the Naked Angels theater company and an associate artist at the Roundabout Theatre Company.

Mantello came to New York from Illinois in 1984 in the midst of the AIDS crisis, having overcome a youthful feeling, he admitted to a reporter in 2013, that "for some reason I was deeply ashamed of the theater early on. I think it had to do with this growing sense I was gay, although I couldn’t have put a word to it back then. Where I grew up, boys played sports. When [teacher] Mrs. Windsor wrote in my yearbook, 'Have you ever considered a career in the theater?' it was literally like she wrote the word 'faggot'."

Mantello began his theatrical career as an actor in Keith Curran's Walking the Dead and Paula Vogel's The Baltimore Waltz. On the transition from acting to directing, Mantello said, "I think I've become a better actor since I started directing, although some people might disagree. Since I've been removed from the process I see things that actors fall into. Now there's a part of me that's removed from the process and can stand back."

Mantello directs a variety of theatre works, as The New York Times noted: "Very few American directors – Jack O'Brien and Mike Nichols come to mind – successfully jump genres and styles the way Mr. Mantello does, moving from a two-hander like Frankie and Johnny in the Clair de Lune to the huge canvas of a mainstream musical comedy like Wicked, from downtown stand-up (The Santaland Diaries) to contemporary opera (Dead Man Walking) to political performance art (The Vagina Monologues)."

A Roundabout Theatre Company revival of Lips Together, Teeth Apart directed by Mantello was scheduled to open at the American Airlines Theatre in April 2010, when one of the stars, Megan Mullally, suddenly quit. The production was postponed indefinitely due to her departure.