Every St. Patrick’s Day for two decades, Gerry Adams or other leaders of Sinn Fein, the party once known primarily as the political arm of the Irish Republican Army, have come to the United States to lobby Washington politicians and rally Irish-American donors.

This year there has been a new item on Mr. Adams’s agenda: passing the torch to the party’s new president, Mary Lou McDonald, 48, whose election last month represented a generational shift at a time of great uncertainty for Northern Ireland.

“We have been blessed with a generational transition,” Mr. Adams, 69, said in a speech in New York on Friday, motioning to Ms. McDonald and her vice president, Michelle O’Neill, 41. “And it is a matter of pride for me that our party chose two women to lead us because women for too long have been written out of our history.”

Mr. Adams, who won a seat in the Irish Parliament in 2011, is a towering — and divisive — figure in modern Ireland. Long accused of having a leadership role in the I.R.A., a charge he denies, he led Sinn Fein for 34 years, most notably through an American-brokered peace process that ended Ireland’s sectarian conflict in 1998.