McGrath's film adaptation differs considerably in content from Southern's novel. Relocated to London in the 1960s, it introduces a homeless orphan whom Sir Guy Grand picks up in a park and on a whim decides to adopt. The role was played by Ringo Starr and written with him in mind. The movie is often remembered for its song "Come and Get It" written and produced by Paul McCartney and performed by Badfinger, a Welsh rock band promoted by Apple Records. The lyrics refer to Grand's schemes of bribing people to act according to his whims ('If you want it, here it is, come and get it'). Thunderclap Newman’s "Something in the Air" is also prominent in the film's soundtrack.
British actor and dancer Lionel Blair was responsible for the film's choreography. A host of British and American actors (see cast) have brief roles in the movie, many playing against type.
Episodic in character, The Magic Christian is an unrelenting and often heavy-handed satire on capitalism, greed, and human vanities. Notable are the appearances of (pre-Monty Python) John Cleese and Graham Chapman (uncredited), who had jointly written an earlier version of the film script — of which only the scenes they appear in survived.
The scene involving the vat containing animal blood, urine and excrement was filmed on London's South Bank on a stretch of wasteground on which the National Theatre was later built. It was originally planned to film this climactic scene at the Statue of Liberty in New York and, remarkably, the U.S. National Park Service agreed to the request. Sellers, Southern and director Joseph McGrath then travelled to New York on the Queen Elizabeth 2 (at a reported cost of US $10,000 ($65,300 today) per person) but the studio then refused to pay for the shoot and it had to be relocated to London.
Sir Guy Grand (Peter Sellers), an eccentric billionaire, together with his newly adopted heir (formerly a homeless derelict), Youngman Grand (Ringo Starr), start playing elaborate practical jokes on people. A big spender, Grand does not mind handing out large sums of money to various people, bribing them to fulfill his whims, or shocking them by bringing down what they hold dear. Their misadventures are designed as a display of father Grand to his adoptive charge that "everyone has their price"—it just depends on the amount one is prepared to pay. They start from rather minor spoofs, like bribing a Shakespearean actor (Laurence Harvey) to strip during a stage performance of Hamlet, and convincing a traffic warden (Spike Milligan) to take back a parking ticket and eat it (delighted by the size of the bribe, he eats its plastic cover too) and proceed with increasingly elaborate stunts involving higher social strata and wider audiences. As their conversation reveals, Grand sees his plots as 'educational.'
At Sotheby's art auction house, it is proudly claimed that an original Rembrandt portrait might fetch £10,000, yet to the astonishment of director Mr. Dugdale (John Cleese), Grand makes a final offer of £30,000 (£445,300 today) for it and having bought it, proceeds, in front of a deeply shocked Dugdale, to cut with his scissors the portrait's nose from the canvas. In a classy restaurant he makes a loud show of wild gluttony, Grand being the restaurant's most prominent customer. In the annual Boat Race sports event, he bribes the captain (Richard Attenborough) of the Oxford team (where Graham Chapman plays a member of the rowing team) and makes them purposely ram the Cambridge boat, to win a screamingly unjust victory. In a traditional pheasant hunt, he uses an anti-aircraft gun to down the bird.
Guy and Youngman eventually buy tickets for the luxury liner The Magic Christian, along with the richest strata of society. Guests seen boarding the yacht include John Lennon and Yoko Ono, and Jacqueline Kennedy and Aristotle Onassis (all played by lookalikes). In the beginning everything appears normal and the ship apparently sets off. Soon, things start going wrong. A solitary drinker at the bar (Roman Polanski) is approached by a transvestite cabaret singer (Yul Brynner), a vampire (Christopher Lee) poses as a waiter, and a cinema film features the unsuccessful transplant of a black person's head onto a white person's body. Passengers start noticing, through the ship's closed-circuit television, that their captain (Wilfrid Hyde-White) is in a drunken stupor and gets carted off by a gorilla. In a crescendo of panic, the guests try to abandon ship. A group of them, shown the way by Youngman Grand, instead reach the machine-room. There, the Priestess of the Whip (Raquel Welch), assisted by two topless drummers, commands more than a hundred slave girls. They are naked except for loincloths. Rowing five to an oar, their wrists are manacled and fastened by chains to the ceiling. As passengers finally find an exit, and lords and ladies stumble out in the daylight, it is discovered that the supposed ship was in fact a structure built inside a warehouse, and the passengers had never left London. As they break out, a large painted sign reading 'SMASH CAPITALISM" can be seen on the inside wall of the warehouse. During the whole misadventure, the Grands look perfectly composed and cool.
Toward the end of the film, Guy fills up a huge vat with urine, blood and animal excrement and adds to it thousands of bank notes. Attracting a crowd of onlookers by announcing "Free money!", Grand successfully entices the city's workers to recover the cash. The sequence concludes with many members of the crowd submerging themselves, in order to retrieve money that had sunk beneath the surface, as the song "Something in the Air" by Thunderclap Newman, is heard by the movie's audience.
The film ends with both Guy and Youngman, having returned to the park where the film opened, bribing the park warden to allow them to sleep there, stating that this was a more direct method of achieving their (mostly unstated) ends.
Most mainstream critics have been quite negative on the film, especially for its extensive use of black humour. Darrel Baxton, in his review for Splitting Image, refers to the film as of 'the school of savage sub-Bunuelian satire'.
Christopher Null in filmcritic.com states that 'it is way too over-the-top to make any profound statement'.
In his seminal book The Celluloid Closet, writer and activist Vito Russo condemns it as "viciously homophobic".The episode of The Simpsons television series entitled "Homer vs. Dignity" (2000) follows the film's plot line.
Writer Grant Morrison named The Magic Christian as an inspiration for his Batman Incorporated series.
The Magic Christian was released on DVD and Blu-ray by Olive Films (under license from Paramount Pictures, whose parent company Viacom owns the Republic Pictures/Melange library, which this film is a part of) on 28 May 2013.