Williams was drawn into the public arena after witnessing the death of three children on 10 August 1976 when they were hit by a car whose driver, an IRA fugitive named Danny Lennon, was fatally shot by British authorities. Their mother, Anne Maguire, (sister of Mairead Corrigan) who was with them, eventually committed suicide in 1980.
Within two days, Williams had obtained 6,000 signatures on a petition for peace and gained media attention. Together with Mairead Corrigan, she cofounded the Women for Peace which later, with co-founder Ciaran McKeown became The Community for Peace People.
The two organized a peace march to the graves of the children, which was attended by 10,000 Protestant and Catholic women. The following week, Williams and Corrigan again led a march — this time with 35,000 strong.
On 13 August, the day of the Maguire children's funeral, Betty Williams and Mairead Corrigan met McKeown, who joined the two women in founding the Peace People. McKeown wrote the original Declaration and organized the rally supporting it.
Since winning the Nobel Peace Prize Williams has received the People's Peace Prize of Norway in 1976 , the Schweitzer Medallion for Courage, the Martin Luther King, Jr. Award, the Eleanor Roosevelt Award in 1984, and the Frank Foundation Child Care International Oliver Award. In 1995 she was awarded the Rotary Club International "Paul Harris Fellowship: and the Together for Peace Building Award.
She heads the Global Children's Foundation and is President of the World Centers of Compassion for Children International. She is also the Chair of Institute for Asian Democracy in Washington D.C. and a Distinguished Visiting Professor at Nova Southeastern University. In 2006, Williams was one of the founders of the Nobel Women's Initiative along with sister Nobel Peace Laureates Mairead Corrigan Maguire, Shirin Ebadi, Wangari Maathai, Jody Williams and Rigoberta Menchu Tum.