The Peace People initially faced down violent opposition by the I.R.A. — participants in the first Peace Women march in Belfast were assaulted, accused of collaborating with the British — but the momentum behind the movement ebbed, and there were disagreements among the three leaders over strategy and funding. Since the late 1970s the organization has had little presence in Northern Ireland.

Ms. Williams, who was criticized for not donating all of her share of the Nobel Prize money to the cause, left the Peace People in 1980 and emigrated to the United States, settling in Florida. She returned to live in the Republic of Ireland in 2004.

Like Ms. Corrigan, Ms. Williams used her profile as a Nobel laureate to campaign on international issues, including children’s welfare and global peace. She lectured widely in the United States.

Relations with Ms. Corrigan, which had become strained as the Peace People flagged, were mended after Ms. Williams’s return to Ireland. In 2006, they joined four other female Nobel laureates to found the Nobel Women’s Initiative, promoting peace, women’s rights and other causes. After a visit to Iraq that same year, Ms. Williams caused controversy when she told a children’s seminar in Australia that she didn’t believe that she was nonviolent.

“Right now, I would love to kill George Bush,” she said, referring to President George W. Bush. “I don’t know how I ever got a Nobel Peace Prize, because when I see children die, the anger in me is just beyond belief. It’s our duty as human beings, whatever age we are, to become the protectors of human life.”

After Ms. Williams’s death, Ms. Corrigan put out a statement of condolence on the Peace People website, saying in part, “Betty was a woman of great courage with a passion for peace and a love and compassion for all children.”