Gruat was born as Hélène Rambaud in Paris on 8 March 1913. Her birthplace was in the Seine department until New Year’s Day 1968, when it was incorporated into Paris. Her occupation was an executive secretary, working in Paris.

Gruat lived independently in Gémenos until 2019 when, at the age of 106, she moved into a nursing home in the commune of Roquefort-la-Bédoule, where she currently resides. On her 108th birthday, it was reported that she was in good health and could still walk.