Louis Cancelmi is an American stage and film actor. He is a frequent performer in productions by the Public Theater, both at their Astor Library home and at the Delacorte Theater in Central Park. He is best known for appearing in Boardwalk Empire (2014), Blue Bloods (2015–2016), The Irishman (2019), and Killers of the Flower Moon (2023).

Cancelmi was born in Pittsburgh. His family relocated to California, then to Anchorage, and then to Seattle, with Anchorage being Cancelmi's self-identified hometown. He is the brother of actress Annie Parisse.

Cancelmi started acting in high school plays. He attended Yale College, entering with interests in writing and mathematics but ultimately majoring in theater.

He is married to Elisabeth Waterston, daughter of Sam Waterston, with whom Cancelmi acted in Please Be Normal in 2014 and Shakespeare in the Park's The Tempest in 2015. The couple lives in the Hudson Valley with their children.