Within hours, her action was, in the eyes of most observers, triumphantly vindicated when the prisoners announced they had dropped their opposition to the talks process and were willing to give negotiations another chance.
Her dramatic action and its equally dramatic result mean that the Stormont multi-party talks will resume on Monday with much of the tension of recent weeks drained from the air.
It is now likely that all eight parties who left the talks before Christmas will be present.
Ms Mowlam's crucial meeting was with five members of the Ulster Defence Association, including Michael Stone, who is serving a battery of life sentences for six murders.
She also, almost in passing, met representatives of the Maze's IRA prisoners, including a man serving life for the murder of two soldiers.
This was clearly a ground-breaking initiative which was last night viewed as a triumph for Ms Mowlam's determination to keep the process going, if necessary using the most unconventional and audacious means.
There were, however, some exceptions to the majority opinion that she had pulled off a spectacular political coup. Lord Alderdice, leader of the moderate Alliance Party, said: "Paramilitaries have hyped the whole situation up and the Secretary of State has fallen into their web. Both she and they can claim a great victory, thoroughly ensconcing them as the important arbiters of our future, not democratic politicians. It has made threats of violence more likely in the future."
His concerns were echoed from the Conservative backbenches by Nicholas Winterton MP, who described the move as "one of the most diabolical instances of pandering to terrorism I can think of." Most of the critics, however, were silenced by the fact her approach brought such a speedy success.
Ms Mowlam gave the UDA prisoners a 14-point statement of government policy which she said contained no guarantees and no concessions to them.
The key section on prison issues declared: "We have a responsibility to maintain community confidence in the criminal justice system and in the political process.
"We are prepared in the talks liaison sub-committee on confidence-building measures to discuss parties' concerns and to work on an account of what would happen in respect of prisoner releases in the context of a peaceful and lasting settlement being agreed.
"But let me be clear there will be no significant changes to release arrangements in any other context or for prisoners associated with a paramilitary organisation actively engaged in terrorist activity."
While this clearly contains no guarantees of any early release programme, the prisoners are believed to have been impressed both by her decision to speak directly to them and by the indication that prisons issues now seem assured of a high place on the talks agenda.
Ms Mowlam said she had received messages from a number of people who had lost relatives in the troubles, adding that she apologised to those who had been offended by her initiative. Many others, she said, were supportive of the move.