The Sunday Independent columnist Eoghan Harris will no longer be writing for the newspaper, its editor has said.
The Irish Independent newspaper reported that the decision to terminate Mr Harris's contract was taken by editor Alan English, after the columnist was found to have been involved in the running of an anonymous Twitter account.
The account, in the name of Barbara J Pym, had tweeted opinions about Irish news and current affairs.
A spokesperson for Twitter said that account referenced, @barbarapym2, has been permanently suspended for violating Twitter's rules on platform manipulation and spam.
The spokesperson said Twitter has also suspended eight other accounts linked to the Barbara J Pym account for violating its policy on platform manipulation and spam.
"Using technology and human review in concert, we proactively monitor Twitter to identify attempts at platform manipulation and mitigate them - we will continue this approach to platform manipulation and any other attempts to undermine the integrity of our service," the spokesperson said.
Speaking on RTÉ's Drivetime programme, Eoghan Harris said he was one of the founders of the "site", but that in recent times he had "moved to the background as more of an advisor".
He said five to six people in total were involved (with the twitter account).
Mr Harris said he was involved with the account as he could not address issues relating to Northern Ireland every week as a political columnist.
He said the other people involved with the account were historians and trade unionists and he said no politicians or journalists were involved. He said the others wanted to stay anonymous because they were "nervous of Sinn Féin".
Mr Harris said he had "very few platforms available to him to express his views".
In relation to a comment made on the account that referenced a female journalist's 'backside', Mr Harris said this was not a sexualised comment and was one that could be said about any male politician.
He said he was one of the only journalists in Ireland who tackled Sinn Féin "at the hard end" and that the account used robust political tweets aimed at "tough political people".
He told RTÉ that "any fair minded person" would see the account as a "generally benign account" and if it did criticise people, they were "Sinn Féin enablers or pawns".
He claimed RTÉ "keeps him off the air" because of his view of Sinn Féin and that he has little profile or support.
Sunday Independent editor, Alan English told the Independent that, having reviewed the Twitter account, he found it frequently went far beyond what he would describe as fair and reasonable comment and that such material would not have been published in the paper or on Independent.ie.
Mr English said the Sunday Independent encouraged the expression of strong, sharp and diverse opinions, and that Eoghan Harris's column had been a must read for a considerable time.
He said his views had long divided opinion, but that freedom of expression was a core principle of the paper and its owner Mediahuis.
However, he said Mr Harris's position as a columnist had become untenable when Mr Harris confirmed he had an involvement in the operation of a fake Twitter account.
Mr English also said he had enjoyed working with one of the most unique voices in Irish public discourse and that, on a personal level, he very much regretted that his involvement with the paper had ended in this way.
Publisher Peter Vandermeersch said: "Eoghan has been an outstanding columnist of the Sunday Independent. While we are very appreciative of his contributions over the years, we expect all our contributors to act in line with our core values of openness, transparency and the highest journalistic standards.
"We could not tolerate a situation where a columnist was contributing anonymously to a social media account which contradicts these core values."
Mr Harris is a former Senator, and previously worked as a current affairs producer with RTÉ.