Bouënnec was born as Marthe Joséphine Mahé in Brest, one of the westernmost towns in mainland France, on 4 April 1906. Her parents were not married at the time of her birth, so her mother’s surname was originally given. On 29 June 1906, her parents’ marriage took place and she was renamed to Chaleyssin.
On 30 August 1928, Bouënnec married her husband, François, a widowed teacher seven years her senior, and later worked as a teacher herself. She lived independently until the age of 104, when she broke her foot as the result of a fall and moved into a Brest retirement home. One of her sons died in 2015 aged 87.
As a centenarian, Bouënnec was reported to be of a solitary nature, not partaking in activities in her retirement home nor having birthday celebrations. She died on 4 August 2016 at the age of 110 years, 122 days.