Prinsley had sought selection as Labour candidate for Great Yarmouth, but was unsuccessful. After the 2024 election was called, the Labour Party told him he had been selected to fight Bury St Edmunds and Stowmarket,[10] and his successful election was seen as a surprise win in an area that has traditionally been heavily Conservative.[11] He defeated Conservative candidate Will Tanner, who had previously served as the Deputy Chief of Staff to Prime Minister Rishi Sunak. He campaigned in an old Post Office van, decorated with photographs of him in surgical scrubs, becoming one of the oldest first-time MPs. He has said that, regarding the jobs of surgeon and MP, 'both of these roles have their uses'.[12]
He is Jewish and attends Norwich Synagogue.[5] His wife, Dr Marian Prinsley, is a retired psychologist and former president of the Norwich Hebrew Congregation who became the Sheriff of Norwich in 2019.[14] Mr Prinsley's brother-in-law is John Schlapobersky, a group psychotherapist and anti-apartheid activist who was a Founding Trustee of the Medical Foundation for Victims of Torture. The Prinsleys have three adult children and are grandparents.[9]
Prinsley is a landlord and co-owns four residential properties which provide a rental income of over £10,000 a year.[15]