The veteran journalist, Eamonn McCann, has stepped down as chairman of the Bloody Sunday Trust.
He said that he had taken his decision for a number of reasons.
"It was a suitable moment for a parting of the ways," he said. "It has been more time and energy consuming than might appear."
He said that he and other members of the Trust had disagreed over a number of issues, but stressed that he parted on good terms.
Mr McCann also said that "on balance", he felt that a controversial march to commemorate the 40th anniversary of the Bloody Sunday march should have been included in the official programme of events.
Thousands of people attended the event on Sunday, which was organised by some of the families of those who died on Bloody Sunday.
The majority of the families said they did not want to take part after what they considered to be the final march last year, following the publication of the findings of the Bloody Sunday Inquiry.
"I think it would have been reasonable to include it," he said.
"But it is also reasonable to say, of course, that the organisers of the week were entitled to decide what should go into the programme and to decide what should go into it whether I or anyone else disagrees with it."
Jean Hegarty, whose brother Kevin McElhinney was shot dead on Bloody Sunday, paid tribute to Eamonn McCann for his contribution over many years.
"If he has decided to step down I can only respect that decision," she said.
"His contribution has just been so enormous over all these years, and he's been an enormous asset in the campaign."