The plot centres around a band of chickens who see a smooth-talking Rhode Island Red named Rocky as their only hope to escape from certain death when the owners of their farm decide to move from selling eggs to selling chicken pot pies.
The film was initially part of a five-picture deal between DreamWorks and Aardman Animations, which was never completed, due to the companies' splitting over 'creative differences'.
The Tweedys are a middle-aged couple who run a struggling chicken farm somewhere in Yorkshire, England, circa the 1950s. Mrs. Tweedy (voiced by Miranda Richardson) is the ill-tempered (she suffers mental breakdown) brains of the pair, while Mr. Tweedy (voiced by Tony Haygarth) is much less intelligent but can readily do the farm's manual work. The coop is run in the style of a World War II POW camp, with the chickens accountable for the number of eggs they lay daily. Their unofficial leader Ginger (voiced by Julia Sawalha) has attempted numerous escapes, often using contraband smuggled in by a pair of rats named Nick and Fetcher (voiced by Timothy Spall and Phil Daniels). However, Ginger is routinely captured by Mr. Tweedy and his dogs and is later thrown into a coal bin for solitary confinement. Ginger is released from the bin just in time for roll call the next day, when Mrs. Tweedy removes one chicken who has laid no eggs for a week and kills her with a hatchet for the Tweedys' dinner. Ginger becomes increasingly desperate to find a plan of escape which will work, but faces problems with Nick and Fetcher, who are tired of being paid with chicken feed and want their own eggs instead.
Mrs. Tweedy soon realises that the couple's farm is failing and reads a catalogue on an ambiguous method of increasing profits. Realising something is wrong, Ginger attempts to rally the other chickens' spirits so they will speed up their efforts to escape. However, she soon concludes that their only viable plan is to go over the fence, something that has not been tried yet. As she sits outside the coop that night, she sees a Rhode Island Red cockerel named Rocky (voiced by Mel Gibson), who hurtles over the fence and crash-lands in the coop. The other chickens fawn over Rocky, while Ginger finds a torn section of a poster that appears to show Rocky flying. After Ginger discovers that Rocky is from a circus, she agrees to hide him from his owners if he teaches them how to fly. Rocky reluctantly agrees, but says he cannot show them immediately because he injured his wing in the crash. Instead, Rocky puts Ginger and the other chickens through a set of exercises that seem to have no purpose, while assuring them that they are making progress.
The chickens are surprised by a large piece of equipment being delivered to the farm, followed by Mrs. Tweedy's order to double their feed rations. Ginger concludes that the Tweedys are trying to fatten the chickens up and then kill them all, leading to an argument between her and Rocky over telling the chickens the truth and not destroying their morale. Discovering that Ginger's news has sent them into a depression, Rocky organises a party using a radio procured by Nick and Fetcher. Rocky's wing has fully healed by now, but before Ginger can persuade him to give a flying demonstration, she is taken by Mr. Tweedy for a test of their new equipment - a machine for making chicken pies.
Rocky rescues Ginger from the machine, sabotaging it in the process so that they will have more time to work on their escape. Fowler (voiced by Benjamin Whitrow), an older cockerel who has been doubtful of Rocky's acts, now begins to respect him and gives Rocky his old Royal Air Force (RAF) badge in tribute. Rocky decides to flee the farm the next day, leaving behind Fowler's medal and the missing section of his poster, which shows that he was actually a stunt cockerel who "flew" by being shot from a cannon. This revelation outrages and demoralises all the chickens except Ginger. When Fowler arrives to try and restore order, he begins talking of his days in the RAF, leading Ginger to realise that she and the other chickens could fly out after all by using an airplane, built from the chicken coops, modeled after Fowler's pictures and personal recollections and constructed using tools supplied by Nick and Fetcher. The chickens race against time to assemble their plane as the Tweedys work to repair their pie machine.
The chickens complete their plane just as Mr. Tweedy enters the coop to grab them. However, the chickens launch an open revolt by tying up and gagging him. As they are preparing to depart, Mr. Tweedy frees himself and knocks down the launch ramp. Ginger jumps down as Fowler turns the plane around, knocking Mr. Tweedy unconscious. Ginger and Rocky - who has just returned to the farm after seeing an ad for the Tweedys' pies - set the ramp back in place and climb aboard the plane, with Mrs. Tweedy grabbing a string of lights hanging from the tail. She is dragged into the air, weighing it down, and Ginger crawls out to try and cut the string. Mrs. Tweedy swipes at her with her earlier-used hatchet, missing her but severing the string, and Ginger lets her fall through the barn and into the pie machine, plugging its safety valve. This causes the machine to build-up pressure and explodes in the mushroom cloud of gravy, destroying the barn leaving only the door standing. Mr. Tweedy reminds his wife about the chickens being organized, This only enrages Mrs. Tweedy wanting to lash out on him. Having enough, Mr. Tweedy pushes the remaining door onto Mrs. Tweedy, killing her in progress and the chickens continue their flight to freedom.
In the epilogue, the chickens have established a sanctuary for themselves, where they can live in comfort and raise their baby chicks. Rocky and Ginger begin a relationship, and Nick and Fetcher discuss the idea of starting a chicken farm of their own. During the closing credits, their talk becomes an argument over whether the chicken or the egg came first.
- Mel Gibson as Rocky the Rhode Island Red (or Rocky Rhodes for short), a cockerel who crash-lands into the farm's chicken coop after fleeing from a circus.
- Julia Sawalha as Ginger, who is determined to save her fellow chickens from their impending doom on the Tweedys' farm. She is usually the one that comes up with the ideas and is generally more intelligent than the other chickens.
- Timothy Spall as Nick, a portly rat who smuggles contraband into the compound.
- Phil Daniels as Fetcher, Nick's slim, slow-witted partner.
- Jane Horrocks as Babs, the fattest of the chickens with a dim-witted innocence and a love of knitting.
- Imelda Staunton as Bunty, the group cynic who is the most skeptical of Ginger's escape plans.
- Miranda Richardson as Malicia Tweedy, a cantankerous egg farmer who decides to convert her farm into a chicken pot pie factory solely for monetary reasons.
- Tony Haygarth as Mr. Willard Tweedy, Melisha's henpecked husband.
- Benjamin Whitrow as Fowler, an elderly cockerel who regularly prattles about his Royal Air Force experiences.
- Lynn Ferguson as Mac, Ginger's brainy Scottish assistant and chief engineer.