Taoiseach Enda Kenny has said his successor's biggest challenge will be to protect Ireland in the event of the British exit from the European Union.
In a letter to the Fine Gael party, Mr Kenny thanked supporters and members for their assistance over the past 15 years.
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Mr Kenny has resigned as leader of the party but will remain as Taoiseach until a successor is appointed on June 2nd.
He wrote: “When I was elected leader of Fine Gael in 2002, our Party was at a very low ebb having just suffered the worst election result in its modern history. Indeed, many commentators went as far as to predict that Fine Gael would slide into political extinction.
“So of course the challenge ahead was not something I underestimated.My promise then was to devote all of my energy to rebuild our Party and to restore its electoral strength. That, I knew, would be a very slow, laborious and difficult task. But as I travelled the length and breadth the country and spoke to so many of you, I knew that you shared my belief that it was possible.”
Mr Kenny said the fruits of Fine Gael’s recovery began in 2004 when the party gained in the local and European elections.
Its biggest electoral success came in the 2011 general election when the party secured 76 seats and became the largest party in Dáil Éireann.
Despite the disappointing results in 2016, Mr Kenny said Fine Gael remained the largest party and was re-elected to Government.
However the Taoiseach insisted the toughest days lay ahead with the challenges of Brexit.
Mr Kenny said this is one of the most pivotal events in modern history which could have unknown challenges for Ireland.
He said: “It is therefore more crucial than ever that the Government continues to work to secure the best possible outcome for Ireland in terms of minimising the impact on our trade and the economy; protecting the hard won peace process in the North; maintaining the Common Travel Area with the UK; and ultimately working to build our own future within the European Union.
“ In that context, it is clear that Brexit and its implications must and will be central to all the work of Government in the time ahead.”
Mr Kenny was leader of Fine Gael for 15 years, a TD for 43 years and Taoiseach for six.
He said that party will continue to grow in his absence but it was time to pass on the baton.
Mr Kenny said: “ I have done my time and my thing, and the country is now better prepared for the future.
"A portrait of Michael Collins has taken pride of place in my office over the past six years, overlooking the day's events. Quietly inspiring, his noble image often brought to my mind his great integrity and dedication, qualities I sought to emulate in my work each day.
“My journey as leader of Fine Gael has not been one I have undertaken alone. I want to thank you now for accompanying me on that journey and for your assistance both to me and to our party in so many ways.
”It has truly been my honour and my privilege.”
The contest to replace Mr Kenny has begun. Leo Varadkar and Simon Coveney are the two contenders.
