Eccentric painter Gulley Jimson (Alec Guinness) is released from a one-month jail sentence for telephone harassment of his sponsor, Mr Hickson (Ernest Thesiger). Nosey Barbon (Mike Morgan), who wants to be Jimson's protégé, greets Jimson at Wormwood Scrubs, but Jimson tries to discourage Nosey from pursuing painting for a living. Jimson steals Nosey's bike to make his way back to his houseboat, which his older lady friend Coker (Kay Walsh) has been maintaining in Jimson's absence.
Jimson tries to borrow money from Hickson and Coker, but Hickson sets the police to trace the phone call. Jimson and Coker later visit Hickson to try to secure advance payment for the early Jimson works. Jimson tries to steal works from Hickson's place but Coker stops him. Hickson and his secretary call the police to have them ejected. Jimson breaks a window, and he and Coker escape via the servant's entrance.
Jimson responds to a note from A. W. Alabaster (Arthur Macrae), secretary to Sir William (Robert Coote) and Lady Beeder (Veronica Turleigh), who are interested in acquiring early Jimson works. One of the early works is in the possession of Jimson's ex-wife, Sara Monday (Renée Houston). Jimson and Coker try to secure an agreement with Sara Monday to obtain that early painting, but are unsuccessful.
When Jimson visits the Beeders, he sees a blank wall in their residence and is immediately inspired to paint "The Raising of Lazarus". He learns that the Beeders are leaving for six weeks, and takes advantage of their absence to execute the painting. An old artistic rival, Abel (Michael Gough), intrudes on Jimson to bring in a large block of marble to fulfil a sculpture commission for British Rail. Jimson pawns the Beeders' valuables, and Abel and Jimson inadvertently destroy part of the Beeders' floor when the marble is accidentally dropped. After Jimson has completed the painting, the Beeders return. Shocked by the painting, they inadvertently fall through the hole in the floor.
Jimson returns to his houseboat and finds Coker there. She was fired from her barmaid job after the press reported the incident at Hickson's residence, and she has nowhere else to live. Later that evening, she surprises Jimson with the news that Hickson is dead and that he has bequeathed his collection of Jimson's works "to the nation". Those works are displayed at the Tate Gallery, which Jimson visits. In the long line to the exhibit, Jimson sees Sara Monday. He then manoeuvres to try to recover that one early work still in her possession. She pretends to agree, and gives Jimson a roll tube. When he returns to the houseboat, however, Coker and Nosey find that the roll contains only toilet paper and not the requested painting. Nosey follows Jimson back to Sara's house. Jimson and Sara struggle over the painting and Sara falls backwards and is knocked unconscious. Jimson and Nosey escape the scene.
Jimson and Nosey seek shelter in an abandoned church. Nosey points out to Jimson a blank wall in the building. Jimson is immediately inspired to execute his largest work, "The Last Judgement". Learning that the church is to be torn down within a fortnight, Jimson, Nosey and Coker recruit local youngsters to help complete the painting. A local council official overseeing the building's demolition objects to their activities. Jimson recruits Lady Beeder to participate, in spite of the injuries he caused her. The painting is completed on the scheduled day of demolition. After the demolition crew warns everyone to stand back, a bulldozer comes crashing through the wall and destroys the painting. Jimson drove the bulldozer, feeling it necessary to destroy the work before anyone else did. As Jimson's admirers pelt the council official and demolition crew in protest, Jimson runs back to his boat and sets sail down the Thames before Nosey and Coker can stop him.
The film featured an Academy Award-nominated screenplay by actor Alec Guinness. Guinness' screenplay generally follows the book it was based on, but Guinness focused on Jimson's character and what it means to be an artist, rather than the social and political themes the book explored. He also deviates from the book's ending, where Jimson had suffered a stroke and was no longer able to paint.
The expressionistic "Jimson" paintings featured in the film were actually the work of John Bratby, a member of the English provincial realist artists known as the Kitchen Sink school.
Mike Morgan fell ill with meningitis shortly before filming ended and died before its completion. As a result, another actor dubbed many of Morgan's lines.
This film has been characterised as "one of the best films ever about a painter". Scott Weinberg of the "Apollo Guide" describes Guinness’ performance as "a devilishly enjoyable character study" that "ranges from 'mildly dishevelled’ to 'tragically exhausted’" and also praises Ronald Neame's direction. Henry Goodman has written of the idea of the artist as destroyer with reference to this film.