Labour MP Jo Cox, 41, has died after being shot in the street outside her constituency advice surgery in Birstall, West Yorkshire Police said.
Cox was in a critical condition after she was shot and stabbed in her constituency by a man reportedly shouting "Britain first".
The alleged gunman has been named locally as Tommy Mair, 52, who neighbours have described as "a loner".
Officers were seen searching his house in Birstall, near the scene of the brutal attack.
Cox, a 41-year-old mother of two, was left lying in a pool of blood on the pavement after her assailant shot and stabbed her outside her advice surgery in the West Yorkshire town. She was MP for Batley and Spen.
Police said a 52-year-old man was arrested in connection with the attack, which happened near the town's library.
Labour leader Jeremy Corbyn said the country would be "in shock at the horrific murder" of Cox, who was a "much loved colleague".