In 1961, D'Arcy joined the anti-nuclear
Committee of 100, a British direct-action group associated with
Bertrand Russell. Her involvement placed her within a strand of Cold War era protest that rejected both nuclear weapons and conventional parliamentary lobbying in favour of civil disobedience. Circa 1968, after relocating to Galway, D'Arcy joined
Sinn Féin. However, she was expelled from the party in 1972 over "political differences". In 1981, her peace activism resulted in imprisonment in
Armagh Women's Prison after she defaced a wall at the
Ulster Museum. During her incarceration, she was held alongside women involved in the
Armagh Prison no-wash protest. Her later account of this period documented the treatment of imprisoned republican women and addressed themes of
Republicanism, state authority, and political imprisonment. From the early 1980s onwards, D'Arcy was involved with the peace movement associated with the
Greenham Common Women's Peace Camp, which opposed the stationing of US cruise missiles at
RAF Greenham Common. She supported and documented the actions of women who engaged in direct action, legal challenges, and sustained protest against nuclear weapons in Britain. From 1987, she engaged in activism around media access and censorship, including running a women's kitchen pirate radio station from her home in
Galway. During the 2000s, D'Arcy became involved in the
Shell to Sea campaign in
County Mayo, supporting local opposition to the Corrib gas project. She participated in solidarity actions and protests connected to Rossport, aligning herself with community-based environmental and anti-corporate activism. In 2010, she became an early signatory to a boycott pledge promoted by the
Ireland Palestine Solidarity Campaign, publicly identifying herself with cultural and political opposition to Israeli state policies towards Palestinians. In 2011, at an
Aosdana meeting, D'Arcy refused to stand for a minute's silence in honour of
Ronan Kerr, a
PSNI officer killed by
dissident republicans. She stated that the refusal was deliberate and political. The action generated significant controversy and public criticism, with some commentators interpreting it as tacit support for armed republican groups, an interpretation she did not accept. In October 2012, alongside Niall Farrell, D'Arcy was arrested after scaling the perimeter fence of
Shannon Airport in protest at its use as a stopover for US military flights. She received a suspended sentence. The protest formed part of her long-standing opposition to Irish facilitation of US military operations. She was released after serving nine and a half weeks of the sentence. In October 2025, she relinquished an honorary doctorate awarded by the
University of Galway in 2022, stating that the decision was a protest against the university's institutional links with Israel. In the same year, she campaigned in support of
Catherine Connolly during the
2025 Irish presidential election. President Connolly visited D'Arcy in hospital two weeks before her death. Until shortly before her death, D'Arcy remained active in anti-war organising, including attendance at peace vigils at Shannon Airport and leafleting in support of Ireland's Triple Lock mechanism on overseas military deployment. ==Death==