Jacobi's talent was recognised by Laurence Olivier, who invited the young actor back to London to become one of the founding members of the new National Theatre, even though at the time Jacobi was relatively unknown. He played Laertes in the National Theatre's inaugural production of "Hamlet" opposite Peter O'Toole in 1963. Olivier cast him as Cassio in the successful National Theatre stage production of "Othello", a role that Jacobi repeated in the 1965 film version. He played Andrei in the NT production and film of "Three Sisters" (1970), both featuring Olivier. On 27 July 1965, Jacobi played Brindsley Miller in the first production of Peter Shaffer's "Black Comedy". It was presented by the National Theatre at Chichester and subsequently in London.