Jonathan Dowdall arrived into Dublin City Council on the crest of a wave of support for Sinn Fein during the last local elections in May 2014.
Dowdall, a former ally of Sinn Fein deputy leader Mary Lou McDonald, got in on the 13th count in the inner city north district.
He was elected alongside his running mate Janice Boylan and Independent councillor Christy Burke, who went on to become Dublin City Lord Mayor.
In September 2014, Mr Dowdall made the decision to step down from his role on the local authority and initially cited health reasons. At the time, Sinn Fein thanked him for his hard work.
However, the following June, the father-of-four told the Herald, he quit Sinn Fein due to bullying within the party.
"There were numerous attacks on myself from a certain element within Sinn Fein, and there were attacks on my team members," he said.
He said after he fell ill the previous year, he was getting calls three or four times a day from Sinn Féin officials instructing him to return to work or give up his seat.
He also claimed he was barred from visiting certain areas of his constituency as it would upset other members of the party.
He said he could not "stand by" while this was going on and took the decision to leave the party.
Sinn Fein strenuously denied the claims and insisted Mr Dowdall never raised any bullying allegations while he was in the party.
Last night, the party said "there was no complaint of bullying made by Jonathan to the party".
A Sinn Fein spokesman said Sinn Féin deputy president Mary Lou McDonald "was aware of personality clashes" in relation to Mr Dowdall.
"Jonathan left Sinn Fein and is part of a rival political grouping in Dublin Central," the Sinn Fein spokesman said.