Harriet Yeo, a former chairwoman of Labour's ruling National Executive Committee, is understood to have resigned her party membership in protest at Ed Miliband's refusal to support an EU referendum.
She also resigned as leader of the Labour group on Ashford Council and will now sit as an independent councillor.
Ms Yeo is the highest profile Labour figure to give her support to Ukip.
And her resignation follows fears within the party that a handful of Euro-sceptic Labour MPs could defect to the anti-Brussels party.
nigel farageGETTY
Mr Farage said he is 'delighted' by Ms Yeo's support
Ukip leader Nigel Farage said: "I'm delighted that UKIP can now count upon the support of such respected figure as Harriet Yeo.
"A life-long trade unionist and Labour Party member who served as Chair of Ed Miliband's NEC she is yet another voice calling for Britain to have a choice about its future.
"We are welcoming support from across the board and Harriet's support is evidence of this."
Ms Yeo was said to have not formally joined Ukip because of links to other independent councillors but will give the party her support in the run up to the general election.
I'm delighted that UKIP can now count upon the support of such respected figure as Harriet Yeo
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