Colum Eastwood is to quit as leader of the SDLP, the PA news agency understands.
Mr Eastwood is expected to announce the decision when he “makes a personal statement” about his future on Thursday, a senior SDLP source said.
The MP for Foyle has been party leader since 2015, having taken over from Alasdair McDonnell following a leadership contest that he won by fewer than 40 votes.
Claire Hanna, the MP for South Belfast and Mid Down, is considered to be among the front runners to be the new leader.
Ms Hanna currently acts as the party’s deputy leader.
Mr Eastwood was returned as the MP for the Foyle constituency at the beginning of July, claiming a majority of just over 4,000 votes.
At the time, he said: “I’m very grateful, mostly to the people of Derry, who have once again said that they want their voice to be heard in Westminster.
“I will gladly continue to be your voice.
“I will stand up for the people of our city, of our constituency. We won’t be quiet.” - PA