Mr Eamon Gilmore has become the fourth Labour TD to declare for the party leadership, for which nominations close on Wednesday.
The Dún Laoghaire deputy said yesterday he was going to run a solo campaign, and would not be pursuing a "dream team" strategy with a candidate for deputy leader.
Meanwhile, the Dublin Central TD, Mr Joe Costelloe, announced yesterday he would be running for the post of deputy leader. Mr Costelloe said he would bring to the job good organisational skills, which were so important to the party at this time.
"The present Fianna Fáil/Progressive Democrat Government is totally bankrupt. It deceived the people in the recent general election and is now making the vulnerable and deprived sectors of our society pay for the extravagance of pet grandiose projects and vote-buying in the run up to the election," Mr Costelloe said.
The entry of Mr Gilmore into the leadership race will set off a battle between himself and his close friend and former Democratic Left colleague, Mr Pat Rabbitte.
Initially it was thought that both TD's would agree between themselves that one would put his name forward for the leadership.
Mr Gilmore said yesterday he wanted to be the first Labour Party Taoiseach .
"To aspire to anything else is to consign Labour to the status of the also rans. I want to haul the Labour party out of third place in Irish politics and to make it the main national alternative to Fianna Fáil."
He said Mr Dick Spring was the most successful leader of the Labour Party due to taking a confident approach. "When Dick Spring said it was possible to make a Labour nominee for President in this country, the people responded. When Dick Spring said he wanted to be Taoiseach of this country, the people responded and gave Labour the largest number of seats it ever had." Mr Gilmore said in an interview on RTÉ Radio one's This Week programme.
Mr Gilmore said the majority of people in this country shared the values of the Labour Party, including equality, inclusiveness and solidarity.
"The people of this country now need a national party to challenge Fianna Fáil and to oppose the deceitful performance of this Government who lied its way back into power." He said there was a need to challenge Fianna Fáil in the interests of democracy.
"The first thing required is belief. We have to believe that the Labour Party is capable of being the national political party capable of challenging Fianna Fáil. It is not healthy for the democracy of this country that for 70 years we had virtual one party rule in this State."
Mr Gilmore said the job of Labour leader was not just a question of opposition in the Dáil or parliamentary performance but was also about building the organisation on the ground, motivating the membership, and inspiring new people to join.
"It is also about developing a new kind of politics. Every other similar party in Europe has found itself at some stage in its development in this position and had to make a breakthrough. I believe the time is right for Labour to make that breakthrough and that is what people want."
The other declared Labour Party leadership candidates are Dublin South West TD, Mr Pat Rabbitte, Wexford TD Mr Brendan Howlin and Dublin North West TD, Ms Roisin Shortall. There was speculation last week that the Westmeath TD, Mr Willie Penrose, would run for the deputy leadership on a ticket with Mr Rabbitte. This combination was seen as one that would strike a balance between urban and rural, Democratic Left and "old Labour" as well as contrasting political styles.
However, Mr Penrose told The Irish Times last night that he would not be making up his mind about declaring for the deputy leadership until today and he denied he would be running on a ticket with anyone.
"If I run I will do so on my own merits and record," he said.
The Dublin West TD, Ms Joan Burton, has also announced she will run for deputy leader.