Manohar Singh was a theatre and film actor. After graduating from the National School of Drama (NSD) in 1971, he began to direct plays for the National School of Drama Repertory. In 1976 Manohar Singh became the chief of the National School of Drama Repertory.

His most memorable performance in theatre was as Tughlaq in the play titled Tughlaq.  The play was directed by his mentor Ebrahim Alkazi, the man who popularised and gave new direction to Indian theatre and gave birth to the National School of Drama.

Under Manohar Singh's leadership, the NSD Repertory scaled new heights, until he quit in 1988 to concentrate on TV and films. However, he never left theatre and gave stellar performances in plays like Pagla Raja (King Lear), Himmat Mai (Brecht's Mother Courage), Begum Barve and Nagamandalam with well-known theatre personalities, Amal and Nissar Allana.

His first film role was in 1978, in the controversial film based on the emergency, Kissa Kursi Ka. He also acted in Govind Nihalani's Party, Mrinal Sen's Ek Din Achanak, Yeh Woh Manzil To Nahin, Rudaali, and Daddy among his more than 25 films. He was also seen in mainstream Yash Chopra films like Chandni and Lamhe. His last film was Everybody Says I'm Fine! in 2001. He also appeared in many TV serials, like Dard and Pal Chhin.

Manohar Singh was awarded the Sangeet Natak Akademi Award in 1982.

He died of lung cancer on 14 November 2002, in New Delhi.