John O'Dowd has received the backing of Sinn Fein colleagues after speaking out to condemn the Kingsmill massacre.
Appearing on BBC's The View programme on Thursday night, the Upper Bann MLA said the IRA killing of 10 Protestant workmen was "shameful" and accepted it was a purely sectarian atrocity.
He said: "Yes. It is shameful what happened on the roadside in south Armagh that night. Absolutely shameful.
"As a republican, I am shamed by it. Those who carried it out should be shamed by it."
Commenting after the programme, Sinn Fein West Belfast MP Paul Maskey tweeted that Mr O'Dowd's appearance had been a "game changer", and Fermanagh and South Tyrone MP Michelle Gildernew retweeted a message that said: "Right tone, correct politics, heartfelt reach and demonstrable leadership."
Mr O'Dowd's comments came as the fallout continued over West Tyrone MP Barry McElduff's video of him posing with a Kingsmill loaf on his head on the anniversary of the 1976 massacre.
He has been suspended by Sinn Fein for three months.
Mr O'Dowd said: "What happened at Kingsmill was wrong, it was sectarian and regardless of who carried it out, whether it was the IRA or others, or people acting from the IRA, it was wrong and we have condemned it in the past.
"And I add my condemnation to it tonight.
"It was wrong when it happened, it's wrong today.
"Those who carried it out did not in any way advance the cause of Irish unity.
"This is why I say I'm not surprised the Kingsmill families are so annoyed and will not believe what Sinn Fein have said, because republicans have hurt them and harmed them.
"But there is a responsibility, a broader responsibility, on unionist politicians, on republican politicians, to move this society forward."
Mr O'Dowd also explained the personal significance of the Kingsmill massacre to him and his family, adding: "I remember Kingsmill very, very well and I tell you why I remember it, because I'd two cousins and an uncle shot dead the night before and I'd another uncle left for dead."
Mr O'Dowd also received praise from Ulster Unionist MLA Doug Beattie, who hailed the "important words and extremely welcome words", which he described as a "positive moment".
The SDLP's Claire Hanna wrote: "... fair to say both John O'Dowd & Edwin Poots stepped out of their comfort zones, to be commended."
Loyalist blogger Jamie Bryson tweeted: "Credit where it is due; @JohnODowdSF could have said very little more last night than he did. He is clearly embarrassed by McElduff."
But south Armagh victims' campaigner Willie Frazer said now was the time for Sinn Fein to admit the IRA was responsible for the atrocity.
"If Sinn Fein were serious in their condemnation of Kingsmill they would offer an apology on behalf of the IRA for not only this brutal attack, but for the sectarian ethnic cleansing campaign in its totality," he said.
Meanwhile, TUV leader Jim Allister said that Mr O'Dowd "belongs to the same Sinn Fein that thought so little of Kingsmill's victims they ducked out of dealing with McElduff".
He added: "Actions speak, not words."