Jude Robinson became the only sitting Labour member of Cornwall Council last night when she took the Camborne North seat in a tight by-election.
She polled 230 votes, compared to 203 votes for the Conservative candidate, Denise Pascoe.
The result represented a 30 per cent swing from the Tories to Labour compared to the last election in 2009.
Anna Pascoe, representing the Liberal Democrats, polled 152 votes, with the Liberal, Mebyon Kernow and Green Party candidates each polling less than 10 per cent of the votes cast.
The turnout for the election was just 21.67%.
The election was called after the resignation of Conservative councillor Bill Jenkins in November last year.