NSW is one step closer to a vote on legalising same-sex marriage, with MPs from across the political spectrum giving the first official notice of new legislation.

A cross-party working group of MPs from the Coalition, Labor, the Greens and an Independent have been working on a bill which would allow gay and lesbian couples to marry in this state, following the failure of three federal same-sex marriage bills earlier this year.

Premier Barry O'Farrell has already confirmed Liberal MPs will be allowed a conscience vote on the bill when it comes before parliament next year, with Deputy Premier Andrew Stoner promising the same for the Nationals. Labor MPs will also be allowed a conscience vote.

Notice will be given of the bill by several MPs in the upper house on Tuesday.

"The co-operative approach being taken here in NSW really shows up Tony Abbott and Julia Gillard for their recalcitrance on marriage equality," said Greens MLC Cate Faehrmann.