SDLP leader Colum Eastwood has confirmed that he has accepted Claire Hanna’s resignation of the party whip.
Her announcement comes after a party meeting in Newry on Saturday in which almost 70% of delegates voted in support of creating a formal partnership with Fianna Fail.
Ms Hanna had previously spoken out against the move.
As well as resigning the party whip she has also resigned as the party’s Brexit spokesperson.
She said she will continue as an ordinary member of the SDLP and as an MLA representing her South Belfast constituents, the BBC reported.
Prior to the conference Ms Hanna said she had a problem with the “exclusivity” of the link with Fianna Fail.
A rival motion on Saturday to further formal links with Fine Gael and the Irish Labour party did not gain adequate support.
In response to her resignation, SDLP Leader Colum Eastwood MLA said: “At the SDLP Special Conference all members were afforded the opportunity to speak and delegates to vote on two motions. The SDLP membership overwhelmingly voted for the party to embark on a partnership with Fianna Fáil.
“It is with regret that we accepts Claire’s resignation. The party membership has democratically spoken and difficult though that decision may be for some, their wishes must be respected and enacted.”