Gertrude was the daughter of Pepin of Landen — Mayor of the Palace and effective ruler of the Frankish kingdom — and his wife the Blessed Itta. At ten, when King Dagobert tried to betroth her to the son of a Frankish duke, she refused publicly at court, declaring herself bound to Christ.
After her father's death in 640, she and her mother founded the great double monastery of Nivelles in Brabant on the model of the Irish foundations (it was placed under the spiritual care of Irish monks brought from Iona by St. Foillan). Gertrude became its abbess at twenty.
She was renowned for hospitality to travelers — Irish monks, Anglo-Saxons crossing to Rome, pilgrims of every nation passed through Nivelles. By the medieval period this gave her the patronage of pilgrims and 'good journeys'; the night-prayer for those traveling, 'Sainte Gertrude soit avec vous,' was widespread across northern France and the Low Countries. The Flemish folk-iconography of cats — Gertrude often shown surrounded by mice — comes from her later association with rodent-killers (and hence cats); she remains one of the few canonized patrons of household cats.
She died at thirty-three after a life of intense ascetic prayer. The Collegiate Church of Saint Gertrude at Nivelles, built over her tomb, was one of the great Romanesque churches of northern Europe until destroyed in 1940.