LONDON — The Irish prime minister, Bertie Ahern, who helped bring peace to Northern Ireland but was dogged by investigations into his personal finances, said yesterday that he would resign next month after 11 years in office.

Mr. Ahern, 56, announced his resignation at a Dublin news conference amid a government tribunal’s probe into whether he received improper cash payments from business executives in the mid-1990s.

In a sometimes emotional 11-minute address, Mr. Ahern denied wrongdoing. But he said the “incessant” attention on his finances had been a drain on his administration. He said the government must “not be constantly deflected by the minutiae of my life, my lifestyle, and my finances.”

“I have never received a corrupt payment, and I’ve never done anything to dishonor any office I have held,” Mr. Ahern said, his voice wavering. “I know in my heart of hearts, I’ve done no wrong and wronged no one.”

The second-longest serving prime minister in Irish history, Mr. Ahern took office in 1997 amid a period of breathtaking economic growth of Ireland.

Mr. Ahern, with his boxer’s build and gregarious personality, built his political career on being a popular and plain-spoken “man of the people.” In his folksy inner-city Dublin accent, he took a moment yesterday to thank the “innately decent” Irish people for all their “cards and letters of goodwill.”

“He has an affectionate following among the voters, who put him in office three times,” an Irish author and historian, Tim Pat Coogan, said. Mr. Ahern remained popular, Mr. Coogan noted, despite growing pressure on him from opposition politicians and members of his own coalition government.