The Expendables, a group of elite mercenaries based in New Orleans, deploy to the Gulf of Aden to save hostages on a vessel from Somali pirates. The team consists of leader Barney Ross, blades specialist Lee Christmas, martial artist Yin Yang, military veteran Gunner Jensen, weapons specialist Hale Caesar, and demolitions expert Toll Road. Jensen instigates a firefight, causing casualties for the pirates. He then tries to hang a pirate, but Yang stops him when Ross and the team discourage it. Ross reluctantly discharges him from the team. Later, Christmas is upset to discover his girlfriend, Lacy, has left him for another man.
Ross and rival Trench Mauser visit "Mr. Church" for a mission. Trench passes the contract to Ross, which is to overthrow dictator General Garza in Vilena, an island in the Gulf of Mexico. Ross and Christmas fly to Vilena for undercover reconnaissance and meet their contact, Sandra, but are discovered. It is revealed that ex-CIA officer James Munroe is keeping Garza in power as a figurehead for his own profiteering operations, while Sandra is revealed to be Garza's daughter. Ross aborts, but Sandra refuses to leave Vilena. Meanwhile, Jensen approaches Munroe to help and Garza is angered further when Sandra is waterboarded for information by Munroe. Meanwhile, Lacy has been physically abused by her new man, so Christmas beats him and his friends, revealing what he does for a living.
Ross and the group discover that Church is a CIA operative and the real target is Munroe, who has gone rogue and joined forces with Garza to keep the drug money that funds the CIA to himself, but the CIA cannot afford a mission to kill one of their own directly because of bad publicity. Ross meets tattoo expert and friend Tool to express his feelings. Tool makes a confession about letting a woman commit suicide instead of saving her. Ross is then motivated to go back for Sandra alone, but Yang accompanies him. Jensen and hired men pursue them on the road, ending in an abandoned warehouse, where Yang and Jensen fight a second time. Ross shoots Jensen when he attempts to impale Yang on a pipe. Jensen makes amends and gives the layout of Garza's palace.
Ross boards the plane with Yang and finds the rest of the team waiting, and they infiltrate Garza's compound. Thinking Munroe hired the team to kill him, Garza has his soldiers' faces painted, preparing them for a fight. The team plants explosives throughout the site but Ross, while saving Sandra, is captured by Munroe's henchmen. The team saves him and kills the Brit, but is pinned down by Garza's men as Paine wrestles Ross. Caesar fights back and Paine escapes. Garza finally stands up to Munroe, ordering him out and returning his money. Instead, as Garza rallies his men against the Americans, Munroe kills him and escapes with Paine and Sandra. Garza's men open fire against the team, who fight their way through, detonating the explosives and destroying the compound. Toll kills Paine by burning him alive while Ross and Caesar manage to destroy the helicopter before Munroe can escape. Ross and Christmas catch up to Munroe, killing him and saving Sandra. Later, Ross gives his mission reward to Sandra to restore Vilena.
In the final scene, the team has returned home and are celebrating at Tool's tattoo parlor with the recovering and now redeemed Jensen. Christmas and Tool play a game of knife throwing, during which Christmas composes a mocking poem about Tool, then throws a bullseye from outside the building.
