Martin Donovan (born Martin Paul Smith; August 19, 1957) is an American actor. He has had a long collaboration with director Hal Hartley, appearing in many of his films, including Trust (1990), Surviving Desire (1991), Simple Men (1992), Amateur (1994), Flirt (1995), and The Book of Life (1998), starring as Jesus Christ in the latter. Donovan played Peter Scottson on Showtime's cable series Weeds. He made his writing/directorial debut with the film Collaborator (2011). Donovan played Detective Hap Eckhart in Christopher Nolan's psychological thriller Insomnia (2002) and the protagonist's CIA handler, Fay, in Nolan's science-fiction thriller Tenet (2020).

Donovan was born Martin Paul Smith in Los Angeles, California, one of four children in an Irish Catholic family. He was raised in Reseda and graduated from Crespi Carmelite High School and attended Pierce College for two years. He attended American Theater Arts, a combined conservatory and theater company in Los Angeles, where he appeared in the plays Richard's Cork Leg by Brendan Behan and Private Life of the Master Race by Bertold Brecht. In 1983, his future wife, Vivian, and he moved to New York City. He joined the off-off-Broadway Cucaracha Theater on Greenwich Street.

Donovan has appeared in 14 episodes of the Showtime television series Weeds, which stars Mary-Louise Parker, for which he was nominated for a SAG Award for Outstanding Performance by an Ensemble in a Comedy Series. He has also acted with Parker in Saved!, Pipe Dream, and The Portrait of a Lady. For the latter, he won the National Society of Film Critics' Award for best supporting actor.

Donovan married actress Vivian Lanko in 1984; they have two sons. They lived in New York City for many years before relocating to Vancouver.