Former republican "supergrass" Raymond Gilmour has said he wants to return to his native Londonderry.
Mr McGuinness said Gilmour must decide whether it is safe to return
He was a member of the INLA and the IRA and his evidence brought dozens of people to trial in the early 1980s.
The case collapsed when the then Lord Chief Justice dismissed his evidence as being "unworthy of belief".
Raymond Gilmour is now asking Sinn Fein leaders to promise he would be safe if he returned to Derry, where he still has relatives.
"I would like Martin McGuinness's assurances, and Gerry Adams's, and whoever else is in charge of Sinn Fein," he said.
'Going into hiding'
"Maybe not to live there, but maybe to come over for a wee holiday, or something like that.
"The only regrets I have are leaving all of my family behind me.
"I am suffering for it now. I have a heart complaint, I'm an alcoholic. You name it - I have all the psychological problems that go along with the things that I have done in the past."
Gilmour said he has not been back to his home city since going into hiding 25 years ago.
Mr Gilmour fled the city in 1982 after giving evidence against 35 republicans.
Martin McGuinness said Mr Gilmour must decide for himself whether or not it was safe to return to Derry and that he was not under threat from Sinn Fein, nor - he believes - from the IRA.
He said if exiles such as Gilmour wanted to return home, it was a matter for their own judgement and their ability to make peace with the community.
The SDLP's Alex Attwood said personal safety for anyone who had been exiled should be guaranteed.
He said they were entitled to return and that there were "no conditions, no constraints, no objections laid on them".
"Everybody in the community must make sure there are no constraints, or restrictions laid on them," he said.