Mr Boakes is believed to have suffered a heart attack
Voters in the North Yorkshire constituency of Thirsk and Malton face a wait to decide who their new MP will be after the death of a candidate.
The UK Independence Party (UKIP) confirmed that their candidate John Boakes, who was in his 60s, had died.
Janet Waggott, acting returning officer for Ryedale District Council, said that meant the election in Thirsk and Malton must be stopped and re-run.
The revised date will be 27 May. Only UKIP will be allowed a new candidate.
Ms Waggott said: "It is very sad and very unusual. It is the first time I have come across this set of circumstances.
"I have spoken to the other four candidates and their agents and explained the circumstances to them.
He was very dedicated to his country and will be greatly missed by all his friends in UKIP
Lord Pearson, UKIP leader
"They are all very sad that somebody has died so suddenly and at such a young age."
Mr Boakes is believed to have suffered a heart attack.
UKIP leader Lord Pearson said: "This is clearly very sad news and our thoughts are with John's family.
"He was very dedicated to his country and will be greatly missed by all his friends in UKIP."
The last time an election was stopped was following the death of Liberal Democrat candidate Jo Harrison in Staffordshire South, in the 2005 general election.
It is only the eighth time polling has been postponed because of a candidate's death since 1918.
Thirsk and Malton is a new constituency, but is notionally a safe seat for the Tories.
The candidates in Thirsk and Malton are: John Clark: Liberal Party; Howard Keal: Liberal Democrat; Anne McIntosh; Conservative; Jonathan Roberts: Labour.