She co-founded, with Betty Williams and Ciaran McKeown, the Women for Peace, which later became the Community for Peace People, an organization dedicated to encouraging a peaceful resolution of the Troubles in Northern Ireland.
Maguire and Williams were awarded the 1976 Nobel Peace Prize.In recent years, she has criticised the Israeli government's policy towards Gaza, in particular to the naval blockade.
In June 2010, Maguire went on board the MV Rachel Corrie as part of a flotilla that unsuccessfully attempted to breach the blockade.