The leader of the Progressive Unionist Party Dawn Purvis has resigned from her party.
She said she was leaving because the PUP was "severely restricted because of its relationship with the Ulster Volunteer Force".
It follows controversy over the shooting of loyalist Bobby Moffett, 43, which has been blamed on members of the UVF.
Ms Purvis had called for an end to intimidation on the Shankill Road.
She said her party supported people's right to attend Mr Moffett's funeral on Friday without fear.
Ms Purvis stepped down on Wednesday evening. She will continue as an independent assembly member at Stormont. She has not ruled out joining either of the main unionist parties long term.
"It's been very difficult but I know that I have made the right decision," she said.
"I believe there are elements within the organisation, that have absolutely no interest in politics or the future of their party and no interest in the PUP."
Ms Purvis said she was leaving "with a very heavy heart".
"I believe the Progressive Unionist Party was founded by individuals who had a real vision for Northern Ireland and a positive and important contribution to make to politics and the peace process in this country. I have been honoured to be a part of that.
"However, I can no longer offer leadership to a political party which is expected to answer for the indefensible actions of others."
Ms Purvis became leader of the PUP following the death of David Ervine in 2007.
In a statement, the PUP said they were losing "a great leader" and wished her well.
PUP councillor John Kyle will act as interim leader.
"It was a very difficult decision Dawn had to make. I fully understood her reasons for making it. All of us who were present felt it was a very sad moment in the history of the PUP," he said.
He agreed that the Moffett murder was "a major factor" in Ms Purvis' decision. But said he was committed to taking over the reins at this stage.
"I'm still committed to the political project. We need to take some time to take stock, review the situation and decide what is the best way to take forward the policies and projects we believe in," he said.
Bobby Moffett was shot dead by two masked gunmen on the Shankill Road last Friday.
A 35-year-old man who was being questioned about the killing has been released. No-one else is being held by police investigating the death.
There is speculation that Mr Moffett may have been involved in a fight with a member of the UVF, but this may have been a personal dispute.
Mr Moffett's mother, Susan, has blamed the UVF for the killing.
BBC NI political editor Mark Devenport said Ms Purvis' resignation was significant.
"Historically, the party has been aligned to the UVF. It is very significant," he said.
"Dawn Purvis was never thought to have the inside track on the paramilitaries that David Ervine had because of his historic track record.
"But she was able to defend his seat. If she has decided she wants to go independent, this presumably would point to the notion that she does believe there is a UVF connection to the shooting."
Tensions have been rising in the area since the shooting on Friday.
The DUP MP for north Belfast, Nigel Dodds said people in the Shankill should be allowed to attend Mr Moffett's funeral on Friday without fear.
Church leaders on the Shankill Road said local politicians also needed to do more to help the community over the coming days.