Cornwall Council's cabinet has voted to spend £536,000 on a bid to win the title for the city of Truro in 2023.
Truro Mayor Rob Nolan said he was only made aware of the "pie in the sky" project when he read about it in the local newspaper on 19 January.
Cornwall Council said the title could "boost the Cornish economy by £100m".
More on the culture bid and other stories from Cornwall
It is still not known whether the EU will proceed with letting the UK host European Capitals of Culture as a consequence of Brexit.
The Department for Culture, Media and Sport, which launched the contest in December, said it was continuing under the assumption that a UK city will host the event in 2023.
Mr Nolan, also a member of Cornwall Council, said he was "astounded" he had not been informed of the bid in the name of Truro.
He said: "It seems to have come out of the blue and off they go spending half a million pounds."
The mayor said he would rather see money spent on supporting existing festivals.
The UK was already lined up to host in 2023 before the country voted to leave the European Union in June.
Cornwall Council did not respond to questions regarding communication with the mayor.
The council was previously awarded £350,000 in 2008 by the European Union in an unsuccessful attempt to lobby for a European Region of Culture designation.
Julian German, the Cornwall Council cabinet member for economy and culture, said: "Cornwall consistently punches above its weight and there has never been a better time for us to celebrate our success."
A mayor has claimed he was "not told" of his city's £500,000 bid to become European Capital of Culture.