A former history teacher, Micheal Martin has led Fianna Fail since February 2011.
The 59-year-old has been TD for Cork South-Central since 1989 and has held a range of ministerial portfolios including enterprise, trade and employment, health and children, and education and science.
In 2004, Mr Martin introduced the ban on tobacco smoking in all Irish workplaces, including pubs and restaurants.
During his tenure as the Republic's minister for foreign affairs, he worked closely with Northern Ireland's political parties and secretaries of state Shaun Woodward and Owen Paterson.
In the nine years since taking over from Brian Cowen, Mr Martin had faced the prospect of being the first Fianna Fail leader to never serve as Taoiseach.
In 2011, the party suffered the worst defeat of a sitting government in the history of the Irish state.
Fianna Fail won only 20 seats, the first time in 79 years that it was not the largest party in the Dail.
However, Mr Martin has remained at the helm and steered the party back to a leading place in the polls in the February 8 election.
Mr Martin has also served as his party's spokesperson on Northern Ireland and has been relentlessly critical of Sinn Fein.
Last December, he said that party proposals for a border poll risked inflaming tensions in Northern Ireland and could be perceived as forcing people into a rushed decision.
A month later, he criticised Sinn Fein as being an anti-European party and said they would not be suitable to be in government in the Republic.
Mr Martin is married to Mary O'Shea and together the couple have had five children.
Their youngest daughter Leana died in October 2010, aged seven, after suffering from a heart condition.
Eleven years earlier they lost a son, Ruairi, in infancy.