Born to a family of minor nobility, Bertrand through his martial abilities would become one of the leading French military figures of the 14th Century.

His initial military service was participation in the Breton Wars of Succession in 1342.

In the period after the Battle of Poitiers (1356) Bertrand came to the attention of Charles the Dauphin of France. When Charles assumed the throne in 1364 he selected Bertrand to join the French force fighting Charles II of Navarre who had laid claim to the Duchy of Burgundy. The French victory over Charles II secured Burgundy for Philip of France.

The late 1360s found du Guesclin fighting in Spain against Pedro I of Castile. However, in 1369 the King of France called him back and promoted him to be Constable of France to resume the war against England.

Despite difficulties with the French nobility regarding his birth, Bertrand lead several successful battles against the English.

Bertrand du Guesclin fell ill and died in 1380.