Newly-elected Fianna Fáil TD Bobby Aylward arrived in Leinster House today on the back of his victory in the Carlow-Kilkenny by-election.
It is the first time since 1996 that the party has won a by-election.
Meanwhile, the row over Senator Averil Power's departure from the party continued.
Ms Power yesterday announced that she was quitting the party and said she will continue in politics as an independent.
Mr Aylward was flanked by supporters and the parliamentary party, minus Senator Power, as he arrived at Leinster House.
He said he would focus on the issues raised by his constituents.
The new deputy was announced and congratulated in the Dáil, but Taoiseach Enda Kenny made reference to the party's recent woes, saying: "You win some, you lose some."
Mr Aylward's director of elections, Barry Cowen, said Ms Power's decision to leave the party had overshadowed his arrival.
However, he said it should not have been the case as he said the party had worked through other divisive referendum campaigns.
Ms Power said the coordinated personal attacks against her over the last 24 hours were hurtful and an attempt by the party to minimise the damage to the party.
Fianna Fáil TDs criticise Power's resignation
Fianna Fáil justice spokesperson Niall Collins today criticised the way Senator Power left the party.
Ms Power had said many Fianna Fáil TDs and senators had not canvassed for the same-sex marriage referendum and that was the "final straw" for her.
Speaking on RTÉ's Today with Keelin Shanley, Mr Collins said that he was disappointed with Ms Power's decision to leave the party and the manner in which she did so.
He also rejected Senator Power's comments that the vast majority of Fianna Fáil public representatives refused to campaign during the referendum.
He defended his involvement in the campaign, saying he was personally engaged in press conferences and media launches.
He said: "I was very disappointed with Averil's decision yesterday and indeed the manner in which she made her announcement without at least giving Micheál Martin the respect that he deserved in terms of contacting him beforehand to discuss it with him, given the amount of political capital Martin invested in Averil Power."
Senator Power has said she feels she has been "personally attacked" by members of Fianna Fáil following her departure from the party.
Speaking on the same programme, she said she is disappointed by the tone from the party after yesterday's events.
Responding to comments made by Mr Collins, she said: "I would have hoped that instead of going on a personal attack that they would have actually dealt with issues that I've raised.
"To say that they didn't know I was unhappy is just completely untrue. I've raised issues at parliamentary parties. It was clear I was unhappy."
Mr Collins said Senator Power never expressed any concern to him, as the party's director of elections, about Fianna Fáil's campaign during that time.
He said Fianna Fáil engaged in a very vibrant campaign right across the country but acknowledged that some party representatives did not pull their weight.
He said: "I think it is fair to say you could point to TDs in all of the political parties ... who you could say allegedly didn't pull their weight.
"From that point of view, she might have a valid criticism there but I think that's a valid criticism for some members within all parties."
Haughey did not canvas for Yes vote
Fianna Fáil councillor for Dublin Bay North Sean Haughey has said he did not canvas for a Yes vote in the same-sex marriage referendum because he did not have the conviction to do so, as he wanted to listen to both sides of the debate.
But he said he had not let his party down by not campaigning.
Mr Haughey said: "I felt that I couldn't canvass with conviction and that I wanted to listen to all the arguments and I listened to the arguments right up to polling day.
"I'm passionate about our country and our society and the way it should develop and at the end of the day, it's a secret ballot."
He also said he was sorry to see Senator Power leave the party.
Mr Haughey said he was confident she would have been on the Fianna Fáil ticket for the constituency in the next general election.
He said while he had not discussed the matter with Mr Martin, he "always felt hopeful that I would come through the convention and I always understood that Senator Averil Power would be added to the ticket and I felt that would be a balanced ticket".
Party activist resigns in Cork
Meanwhile, the Fianna Fáil organisation in Cork city and county has been dealt a blow with the resignation of party activist Ken Curtin.
Mr Curtin, who was Fianna Fáil's Public Relations Officer for Cork East and secretary of the party's Cobh Cumann, announced on social media that he was resigning from both positions and from the party.
I've been crying a lot over last few days but today I'm crying having made a hugely tough decision to walk away from the party I loved
— Ken Curtin (@kencurtin) May 26, 2015Mr Curtin led the Yes Equality Cork campaign and had expressed disquiet at the lack of party support on the ground for the campaign.
He had flagged at the weekend that he would be considering his position.
He said he had reached his decision independently of Ms Power.
Mr Curtin said he felt that Fianna Fáil was no longer a right fit for him and for people with a more liberal outlook.
He said their voices are being drowned out by very elderly, conservative voices.
