The film received three Academy Award nominations and an enthusiastic critical reception.
During the Mexican Revolution, Rancher J.W. Grant hires four men, who are all experts in their respective fields, to rescue his kidnapped wife, Maria from Jesus Raza, a former revolutionary leader-turned-bandit.
Henry "Rico" Fardan is a weapons specialist, Bill Dolworth is an explosives expert, the horse wrangler is Hans Ehrengard, and Jake Sharp is a traditional Apache scout, skilled with a bow and arrow. Fardan and Dolworth, having both fought under the command of Pancho Villa, have a high regard for Raza as a soldier. But as cynical professionals, they have no qualms about killing him now.
After crossing the Mexican border, the team tracks the bandits to their hideout. They witness soldiers on a government train being massacred by Raza's small army. The professionals follow the captured train to the end of the line and retake it from the bandits. Some move on to the bandit camp and observe Raza and his followers—including a female soldier, Chiquita. At nightfall, Fardan infiltrates Raza's private quarters but he is stopped from killing him by Maria, the kidnapped wife. Dolworth concludes, "we've been had."
Fardan escapes with Grant's wife. Back at the train, they find that it has been retaken by the bandits. After a shootout, they retreat into the mountains, pursued by Raza and his men. The professionals evade capture by using explosives to bring down the walls of a gully, thus blocking the bandits' path and delaying their pursuit. It is then revealed that they had not rescued Grant's kidnapped wife but Raza's willing mistress. Grant "bought" Maria for an arranged marriage only for her to escape and return to her "true love" in Mexico.
As Raza and his bandits pursue the retreating professionals, Dolworth fights a rearguard action to allow the other professionals to escape with Maria. In the battle, Raza is wounded. As he and Chiquita attempt to escape, she is shot by Dolworth. Weakened, Raza is captured by Dolworth.
The professionals, with Maria and Raza, reach the U.S. border to be met by Grant and his own men. Grant tells Fardan that their contract has been satisfactorily concluded, even before Maria is safely handed over to him. As Maria tends the wounded Raza, Grant says to one of his men, "Kill him." Before the man can fire, the gun is shot out of his hand by Dolworth. The professionals step in to protect Maria and Raza. They collect the wounded Raza, put him on a carriage and, with Maria at the reins, send both back to Mexico.
Grant calls Fardan a bastard, to which Fardan retorts: "Yes, sir, in my case an accident of birth. But you, sir, you are a self-made man." The professionals follow the departing carriage to Mexico.Burt Lancaster as Bill Dolworth
Lee Marvin as Henry 'Rico' Fardan
Claudia Cardinale as Mrs. Maria Grant
Robert Ryan as Hans Ehrengard
Woody Strode as Jake Sharp
Jack Palance as Jesus Raza
Ralph Bellamy as Joe Grant
Joe De Santis as Ortega
Rafael Bertrand as Fierro
Marie Gomez as Chiquita
The film was adapted for the screen by its director Richard Brooks, who based the screenplay on the novel A Mule for the Marquesa by Frank O'Rourke.
The movie, which was shot in Technicolor, was filmed on location in Death Valley, Valley of Fire and around Coachella Valley in California. The rail scenes were filmed on Kaiser Steel's Eagle Mountain Railroad. The steam locomotive seen in the movie currently resides on the Heber Valley Railroad.
During filming, the cast and crew stayed in Las Vegas. Actor Woody Strode wrote in his memoirs that he and Marvin got into a lot of pranks, on one occasion shooting an arrow into Vegas Vic, the famous smiling cowboy neon sign outside The Pioneer Club.
The musical score was composed by Maurice Jarre.
By 1976 it was estimated the film had earned $8.8 million in rentals in North America.
It was the ninth most popular movie at the French box office in 1966, after La Grande Vadrouille, Dr Zhivago, Is Paris Burning?, A Fistful of Dollars, Lost Command, A Man and a Woman, For a Few Dollars More and The Big Restaurant.
The film received three nominations at the 1967 Academy Awards. Writer and director Richard Brooks, for Best Director and Best Writing (Adapted Screenplay) and cinematographer Conrad Hall, for Best Cinematography.
The film won two Motion Picture Magazine Laurel Awards in 1967, for Best Action Drama and Best Action Performance for Lee Marvin. In Germany, it was one of only four movies to receive a Golden Screen Award (the others were Doctor Zhivago, Merveilleuse Angélique and You Only Live Twice) in 1967.