A team of elite mercenaries, the Expendables, are deployed to the Gulf of Aden off the coast of Somalia to halt local pirates from executing the hostages on a naval ship. The team consists of leader Barney Ross (Sylvester Stallone), former SAS soldier and blades specialist Lee Christmas (Jason Statham), martial artist Yin Yang (Jet Li), sniper Gunner Jensen (Dolph Lundgren), weapons specialist Hale Caesar (Terry Crews) and demolitions expert Toll Road (Randy Couture). Jensen instigates a firefight, causing casualties for the pirates. Yang and Jensen fight over a moral disagreement about hanging a pirate, with Ross finally intervening. As a result of his psychological problems and drug use, Ross reluctantly releases Jensen from the Expendables. The team then travels to New Orleans where they are stationed.
Ross and rival mercenary leader Trent Mauser (Arnold Schwarzenegger) visit a church to meet a man, who takes the name “Mr. Church” (Bruce Willis). Church offers them a mission in Vilena, a fictional island in between the Gulf of Mexico and South America, to overthrow a brutal dictator, General Garza (David Zayas). Busy with other things, Trent gives the contract to Ross. Meanwhile, Christmas visits his girlfriend, Lacy (Charisma Carpenter), whom he discovers has left him for another man. He leaves in a fit of rage, while Lacy insists her actions occurred because she does not see Christmas often and does not even know what he does for a living.
Ross and Christmas fly to Vilena to do initial reconnaissance after meeting their contact, Sandra (Gisele Itié), only for the mission to go awry. Ross learns that Garza is backed by ruthless ex-CIA agent James Munroe (Eric Roberts) as well as his henchmen Paine (Steve Austin) and The Brit (Gary Daniels), who manipulate and keep Garza in power by making his people fear him. Sandra is revealed to be Garza’s daughter. Ross decides to abort and causes casualties among the army as they escape, but Sandra refuses to leave. Meanwhile, a vengeful Jensen approaches Garza and Munroe to help their side.
Christmas visits Lacy again to find that her new boyfriend has beaten her after realizing she was Christmas’ girlfriend and believed she was unfaithful to him and about to go back to Christmas. Christmas beats him and his friends, showing Lacy what he does for a living and winning her over. Later, Ross, Christmas, and Yang deduce that Mr. Church is a member of the CIA and that the real target is Munroe, as the CIA could not kill one of their own by sending in the special forces or the Navy Seals. Ross meets mission coordinator and former teammate Tool (Mickey Rourke) to vent his feelings of guilt. Tool makes an emotional confession to Ross about letting a woman commit suicide during the Bosnian War, and how he felt that if he had saved her, he could’ve saved what was left of his soul. Hearing this, Ross decides to go back for Sandra, telling Christmas and Yang he will do it alone. Yang however tags along; while driving they are chased on the road by Jensen in a shootout. The pursuit ends in an abandoned warehouse, where Yang and Jensen fight a second time. Jensen attempts to impale Yang on a pipe, only to be shot by Ross. A wounded Jensen makes amends and gives the layout of Garza’s palace before he was arrested. Ross boards the plane with Yang and finds the rest of team, ready to aid their friend.
The Expendables infiltrate Garza’s compound. Christmas, Yang, Caesar, and Toll plant explosive charges throughout the site. When Garza has a change of heart after Munroe tortures his daughter and realized he had changed for the worst, Munroe kills him for his treachery, causing Garza’s loyal men to think it was the Expendables who killed him and scatter in rage. The entire team fights and shoots their way through Garza’s soldiers. Ross and Caesar manage to destroy the helicopter Munroe was to escape on. Christmas and Yang manage to kill The Brit while Toll kills Paine. Ross and Christmas catch up to Munroe and kill him, saving Sandra. Instead of taking the payment for the mission, Ross gives it to Sandra to restore Vilena. The team travels back to New Orleans and celebrate their victory at Tool’s tattoo parlor, with the reformed and recovering Jensen. Christmas and Tool challenge each other to a game of knife throwing and Christmas recites a limerick about his respect for Tool, before throwing the knife perfectly in the center of the board.