In 1285, Robert went on crusade to Aragon, as a squire to his uncle Clermont de Nesle, following the massacres of the Sicilian Vespers in 1282.

During August 1322, Robert accompanied his father-in-law Henri de Sully and other French knights into the service of King Edward II of England.

In 1328, the Marshal returned to Flanders following a new revolt of the Flemish, this time accompanied by the new King Philip VI of France.

The Flemish rebels commanded by Nicolaas Zannekin were annihilated by the French royal army at the Battle of Cassel.

Following the outbreak of the Hundred Years' War between France and England, Bertrand was ordered to occupy the island of Guernsey from the English.

Robert resigned his office as Marshall of France in March 1344, aged 71, remaining a member of the King's Council.

The English looted and sacked Caen, with the city burned, 95 French knights and Norman prisoners and 2,500 dead.