Update 4.38pm: Stephen Donnelly has said that Fianna Fáil is the best-placed party to deal with the crises facing the country.
He was unveiled as the party's newest recruit and Brexit spokesman today, just five months after leaving the Social Democrats.
Donnelly said he would not retract previous statements where he had criticised Fianna Fail's role in the economic crash.
"Turn on your television and watch a new channell for one hour and you'll see the challenges we face," he said.
"So the decision for me was very simple - who are thebest team that most closely allign with mu policitcs who I beleive are taking these challenges very seriously, who are coming up with ideas to take on these challenges and oppurtunities, and that very clearly for me is Fianna Fáil."
UPDATE 3PM: Stephen Donnelly has suggested that his supporters in Wicklow wanted him to make a difference - and that’s why he’s joining Fianna Fáil.
Donnelly is being unveiled as the party’s new Brexit spokesman at Leinster House.
In a press conference, which is still underway at Leinster House, he says he’s more worried about the country now than he was when he first entered politics six years ago.
But he’s also said he won’t retract his previous comments where he criticised the party in which he now serves.
Speaking at the press conference he said his supporters continually supported his position as an independent but but urged him to join a party.
"The country is in trouble. There is really serious things coming our way." he said.
More to follow shortly ...
Update 2.10pm: Fianna Fáil Leader Micheál Martin to hold a press conference at 2.30pm just hours after it was announced Stephen Donnelly has joined Fianna Fáil. More to follow ...
Update 1pm: Stephen Donnelly has joined Fianna Fáil just months after leaving the Social Democrats, writes Elaine Loughlin.
The Wicklow TD, who stepped down as joint leader of the Social Democrats five months ago, has now been formally accepted into the Fianna Fáil party.
This morning, the Fianna Fáil Whip Michael Moynihan TD received a letter Mr Donnelly TD applying to join the parliamentary party.
The application was discussed at this meeting and was then formally proposed and approved unanimously.
Fianna Fáil leader Micheál Martin said: “As part of our rebuilding process over the last number of years, Fianna Fáil have made it clear that we welcome new people and new ideas. That message has resonated across the country and in the 2016 General Election we saw the election of an energetic and talented Fianna Fáil team to both Houses of the Oireachtas.
“That process of rebuilding continues and the decision of Deputy Stephen Donnelly to join our team is very encouraging."
He added that Mr Donnelly has made "a serious impact nationally" in his time as a TD.
"In his various roles he has demonstrated a commitment to the principles of fairness and social democracy that underpin the values and policies of the Fianna Fáil party and I know that he will be a strong addition to our existing team, working alongside Pat Casey in Wicklow and nationally," Mr Martin said.
Update 12.35am: Social Democrats TD Catherine Murphy says she’s not surprised that her former party colleague Stephen Donnelly is joining Fianna Fail.
Social Democrats co-founder Catherine Murphy, says she actually thought Stephen Donnelly would have joined another party sooner.
"I’ve got say I’m not hugely surprised. Probably if I’m surprised about anything is that it didn’t happen a little bit sooner, but that’s how things are."
EarlierThe Fianna Fáil parliamentary party has been told Stephen Donnelly has applied for membership.
The news was announced at a closed meeting of Fianna Fail TDs and Senators in Leinster House this morning.
Mr Donnelly was first elected to the Dail in 2011 as an Independent for Wicklow.