In Crouch End, London, electronics salesman Shaun has no direction in his life. He is disrespected by his colleagues, especially Noel, does not get along with his stepfather, Philip, and is dumped by his girlfriend, Liz. Heartbroken, Shaun gets drunk with Ed, his slacker best friend, at their favourite pub, the Winchester. At home, Shaun and Ed's flatmate, Pete, complains of a bite wound from a mugger and berates Shaun into getting his life together.
By morning, a zombie apocalypse has overwhelmed London. Shaun and Ed are slow to notice until they encounter two zombies in their garden, whom they beat to death with a shovel and cricket bat. They devise a plan to rescue Liz and Barbara, Shaun's mother, and then wait out the crisis in the Winchester. They escape in Pete's car and pick up Philip, who's already been bitten, and Barbara. They then use Philip's car to pick up Liz and her flatmates, David and Dianne. Philip reconciles with Shaun before becoming a zombie.
The group abandon the car and sneak through their London neighbourhood, running into friends and evading zombies by imitating them. They take refuge inside the Winchester, where Shaun discovers that the Winchester rifle above the bar is functional. Barbara reveals she was bitten along the way, and dies after giving Liz and Shaun's relationship her approval. David attempts to shoot Barbara, but Shaun stops him, causing the group to argue: Shaun accuses David of being in love with Liz, which Dianne admits. Shaun, distraught, is forced to shoot Barbara when she reanimates.
Zombies break into the pub, devouring David, and Dianne rushes into the horde in an attempt to avenge him. The zombified Pete appears and bites Ed, and Shaun shoots and kills Pete. Shaun, Liz, and Ed take cover behind the bar, which Shaun sets ablaze before the trio take refuge in the cellar. Realising they only have two bullets left, Shaun and Liz contemplate suicide while Ed elects to be devoured by the zombies. Shaun discovers a keg lift that opens out onto the street, and Ed volunteers to stay with the rifle as the zombies break in. The arriving British Army guns down the horde, and take Shaun and Liz to safety.
Six months later, civilisation has returned to normal, and surviving zombies are used as cheap labour and entertainment. Liz has moved in with Shaun, and Shaun keeps the zombified Ed tethered in his shed, where they play video games together.
Simon Pegg as Shaun
Nick Frost as Ed
Kate Ashfield as Liz
Lucy Davis as Dianne
Dylan Moran as David
Penelope Wilton as Barbara
Bill Nighy as Philip
Jessica Stevenson as Yvonne
Peter Serafinowicz as Pete
Rafe Spall as Noel
Martin Freeman as Declan
Reece Shearsmith as Mark
Tamsin Greig as Maggie
Julia Deakin as Yvonne's mum
Matt Lucas as Cousin Tom