Celia Kitzinger, 48, and Sue Wilkinson, 51, who married in 2003 in Canada, say that a failure to recognise the validity of their lawful union constitutes a breach of their human rights.
The couple, who are British and live in Yorkshire, are seeking a legal declaration of the validity of their Canadian marriage in the UK. Papers have been lodged at the Family Division of the High Court in London and the case is expected to be heard early next year.
The two say that under new legislation, which comes into force in December, they will only be given "second-class status". They will be able to register their relationship under the new Civil Partnership Act as a "civil partnership" and receive many of the legal benefits available to heterosexual married couples. But Ms Kitzinger and Ms Wilkinson, both university professors, believe civil partnership to be both "symbolically and practically a lesser substitute".
They said in a statement: "Civil partnerships are an important step forward for same-sex couples, but they are not enough. We want full equality in marriage."
The court will be asked to recognise their overseas marriage in the same way that it would recognise that of a heterosexual couple.
They will argue that failure to do so would constitute a breach of their human rights to privacy and family life and their right to marry, and is discriminatory on the basis of their sexuality.