The UK Independence Party (Ukip) is to be taken to the High Court by the West Midlands MEP claiming it discriminated against her because she is gay.
Nikki Sinclaire is taking action over Ukip withdrawing the whip from her in the European Parliament and preventing her standing for the Commons as a candidate for the party.
She claimed that her treatment had been in breach of Ukip's constitution and was motivated by sexual orientation discrimination.
A directions hearing is to be held by the High Court. The MEP is also taking the party to an employment tribunal, with a preliminary hearing on December 28.
Ms Sinclaire was kicked out of the party after she refused to sit with the eurosceptic group Europe of Freedom and Democracy (EFD) which Ukip joined in the European Parliament last year.
She said she quit the EFD because it contained "extreme elements", including people with "openly homophobic opinions".
"I think that is homophobic in itself, the fact that they expected me to sit next to such people and engage with such people in the Parliament, while taking a holier-than-thou attitude to parties like the BNP (British National Party) in the UK," she said.
As well as withdrawing the whip from the MEP, Ukip's national executive committee also ended her position as the party's candidate for Meriden at the general election.
She said she still believed in the aims of Ukip, whose principal goal is to take the UK from the European Union, and would be prepared to be one of its MEPs again if it was "more tolerant".
"It is unacceptable in the 21st century for people to be marginalised and treated in an offensive and derogatory way on the grounds of their sexuality," the MEP said.