Hughes was born as Máirín O’Sheehan in Belfast, Northern Ireland (then Ireland), on 22 May 1914. She had three siblings: Ruaridh, Conn, and Elizabeth. Her father, Liam O’Sheehan, worked as a customs officer in Dublin, where she spent her early years. Later, the family moved to Killarney, County Kerry, where Hughes grew up.

Hughes recalled her mother looking after inflicted people during the 1918 Spanish Flu in Ireland, as well as Black and Tan constables patrolling in Killarney during and after the Irish War of Independence, and Free State soldiers arriving in 1922.

In 1935, Hughes graduated from University College Cork (UCC) with a degree in science. Three years prior, she had attended the Eucharistic Congress with her family. She worked as a chemist at UCC’s medical laboratory until her marriage to Frank Hughes in 1950, when they moved to Dublin and she became a secondary school science teacher. Her husband worked as a clerical officer for the state transport company; they did not have children. She was widowed in 1986.

Hughes was an avid nature lover, as well as devoutly religious; she enjoyed giving back to her community. For over 30 years, Hughes lived in a nursing home in Chapelizod, Dublin. She played Scrabble and completed crosswords regularly.

In 2018, Hughes was honoured with a UCC Alumni Achievement Award.

A week after turning 109, Hughes was invited to tea with President Michael D. Higgins. She died on 5 September 2023 after a brief illness at the age of 109 years, 106 days. She was survived by a niece and a nephew, Nuala and Michael.