Wednesday's announcement came a day after Ahern, 56, began a court challenge to limit the work of a public inquiry probing payments he allegedly received from a property developer between 1989 and 1992.
Ahern has been leader of his party, Fianna Fail, since 1994 and heads the present coalition government.
"It had always been my intention to review my position as Taoiseach and leader of Fianna Fail in the aftermath of next summer's local and European elections," he said.
"But having reflected on the need to ensure that the work of my ministerial colleagues is not distracted from incessant publicity about the tribunal, I have decided of my own volition to bring forward the date.
"I know that some people will feel that some aspects of my finances are unusual. All of these issues arose in a period when my family, personal and professional situations were rapidly changing and I made the best decisions I could in the circumstances in which I found myself.
"I know in my heart of hearts that I have done no wrong and wronged no-one."
Ahern will be remembered for his role with Tony Blair, the former British prime minister, in helping Northern Ireland's feuding parties reach a workable peace settlement
His conservative views on issues such as abortion, contraception and divorce helped Ahern became the youngest-ever leader of Fianna Fial at the age of 43.
One of his mentors was Charles Haughey, the disgraced late prime minister, who took large amounts of money from businessmen and called Ahern the "most cunning, the most ruthless, the most devious of them all".
Ahern has presided over an economic boom which has seen the standard of living in Ireland greatly improve.
But recently the economy has shown signs of flagging.