[2] He has appeared in numerous Shakespearean stage productions including Hamlet, Much Ado About Nothing, Macbeth, Twelfth Night, The Tempest, King Lear, and Romeo and Juliet.

[5][6] Jacobi has acted in numerous films including Othello (1965), The Day of the Jackal (1973), Henry V (1989), Dead Again (1991), Hamlet (1996), Nanny McPhee (2005), The Riddle (2007), My Week with Marilyn (2011), Anonymous (2011), Cinderella (2015), and Murder on the Orient Express (2017).

Jacobi has also earned two Screen Actors Guild Awards along with the ensemble cast for Robert Altman's Gosford Park (2001), and Tom Hooper's The King's Speech (2010).

As a result of his performance of Edward II at Cambridge, Jacobi was invited to become a member of the Birmingham Repertory Theatre immediately upon his graduation in 1960.

[2] Olivier cast him as Cassio in the successful National Theatre stage production of Othello, a role that Jacobi repeated in the 1965 film version.

In 1972, he starred in the BBC serial Man of Straw, an adaptation of Heinrich Mann's book Der Untertan, directed by Herbert Wise.

Most of his theatrical work in the 1970s was with the touring classical Prospect Theatre Company, with which he undertook many roles, including Ivanov, Pericles, Prince of Tyre and A Month in the Country opposite Dorothy Tutin (1976).

Jacobi was increasingly busy with stage and screen acting, but his big breakthrough came in 1976 when he played the title role in the BBC's series I, Claudius.

In 1986, he made his West End debut in Breaking the Code by Hugh Whitemore, starring in the role of Alan Turing, which was written with Jacobi specifically in mind.

He appeared in the television dramas Inside the Third Reich (1982), where he played Hitler; Mr Pye (1985); Little Dorrit (1987), based on Charles Dickens's novel; and The Tenth Man (1988) with Anthony Hopkins and Kristin Scott Thomas.

Jacobi continued to play Shakespeare roles, notably in Kenneth Branagh's 1989 film of Henry V (as the Chorus), and made his directing debut as Branagh's director for the 1988 Renaissance Theatre Company's touring production of Hamlet, which also played at Elsinore and as part of a Renaissance repertory season at the Phoenix Theatre in London.

The 1990s saw Jacobi keeping on with repertoire stage work in Kean at The Old Vic, Becket in the West End (the Haymarket Theatre) and Macbeth at the RSC in both London and Stratford.

He was appointed the joint artistic director of the Chichester Festival Theatre, with the West End impresario Duncan Weldon in 1995 for a three-year tenure.

Jacobi's work during the 1990s included the 13-episode series TV adaptation of the novels by Ellis Peters, Cadfael (1994–1998) and a televised version of Breaking the Code (1996).

Film appearances of the era included performances in Kenneth Branagh's Dead Again (1991), Branagh's full-text rendition of Hamlet (1996) as King Claudius, John Maybury's Love is the Devil (1998), a portrait of painter Francis Bacon, as Senator Gracchus in Gladiator (2000) with Russell Crowe, and as "The Duke" opposite Christopher Eccleston and Eddie Izzard in a post-apocalyptic version of Thomas Middleton's The Revenger's Tragedy (2002).

At the 53rd Primetime Emmy Awards, Jacobi won an Primetime Emmy Award for Outstanding Guest Actor in a Comedy Series[12] by mocking his Shakespearean background in the television sitcom Frasier episode "The Show Must Go Off", in which he played the hammy, loud, untalented Jackson Hedley, a television star with a misguided belief that he deserves a revival of his stage career.

Therein he played Martin Bannister, an ageing writer who makes up stories about "the Doctor", a character who travels in time and space, the premise being that the series had never made it on to television.

In February 2007, The Riddle, directed by Brendan Foley and starring Jacobi, Vinnie Jones, and Vanessa Redgrave, was screened at Berlin EFM.

In 2011, he was part of a medieval epic, Ironclad, which also starred James Purefoy and Paul Giamatti, as the ineffectual Reginald de Cornhill, castellan of Rochester castle.

Jacobi starred in Michael Grandage's production of King Lear (London, 2010), giving what The New Yorker called "one of the finest performances of his distinguished career".

[20] In 2022, Jacobi appeared in Allelujah, a film adaptation of Alan Bennett's play of the same name directed by Richard Eyre, which also starred Jennifer Saunders, Bally Gill, Russell Tovey, David Bradley, and Judi Dench.

[28][29] In 2007, Jacobi and fellow Shakespearean actor and director Mark Rylance initiated a "Declaration of Reasonable Doubt" on the authorship of Shakespeare's work, to encourage new research into the question.