Charles was born in Évreux. Since his father was first cousin to King Philip VI of France, and his mother, Joan II of Navarre, was the only child of King Louis X, Charles of Navarre was ‘born of the fleur de lys on both sides’, as he liked to point out, but he succeeded to a shrunken inheritance as far as his French lands were concerned.
Charles was raised in France during childhood and up to the moment he was declared king at 17, so he probably had no command of the Romance language of Navarre at the moment of his coronation.
In October 1349, he assumed the crown of Navarre. In order to take his coronation oath and be anointed, Charles II visited his kingdom in summer 1350. For the first time, the oath was taken in a language other than Latin or Occitan as it was customary.
Apart from short visits he spentthe first 12 years of his reign almost entirely in France; he regarded Navarre principally as a source of manpower with which to advance his designs to become a major power in France.
He hoped for a long time for recognition of his claim to the crown of France (as the heir-general of Philip IV through his mother, and a Capetian through his father). However, he was unable to wrest the throne from his Valois cousins.
Charles II served as Royal Lieutenant in Languedoc in 1351 and commanded the army which captured Port-Sainte-Marie on the Garonne in 1352.
The same year he married Joan of Valois, the daughter of King John II of France. He soon became jealous of the Constable of France, Charles de La Cerda, who was to be a beneficiary of the fiefdoms of Champagne, Brie, and Angoulême. Charles of Navarre felt he was entitled to these territories as they had belonged to his mother, the Queen of Navarre, but they had been taken from her by the French kings for a paltry sum in compensation.
After publicly quarrelling with Charles de la Cerda in Paris at Christmas 1353, Charles arranged the assassination of the Constable, which took place at the village of l’Aigle (8 January 1354), his brother Philip, Count of Longueville leading the murderers.
Charles made no secret of his role in the murder, and within a few days was intriguing with the English for military support against his father-in-law King John II, whose favourite the Constable had been.
John II was preparing to attack his son-in-law’s territories, but Charles’s overtures of alliance to King Edward III of England led John instead to make peace with the King of Navarre by the Treaty of Mantes of 22 February 1354, by which Charles enlarged his possessions and was outwardly reconciled with John II. The English, who had been preparing to invade France for a joint campaign with Charles against the French, felt they had been double-crossed: not for the last time, Charles had used the threat of an English alliance to wrest concessions out of the French king.
Relations between Charles and John II deteriorated afresh and John invaded Charles’s territories in Normandy in late 1354 while Charles intrigued with Edward III’s emissary, Henry of Grosmont, 1st Duke of Lancaster at the fruitless peace negotiations between England and France held at Avignon in the winter of 1354–55. Once again Charles changed sides: the threat of a renewed English invasion forced John II to make a new agreement of reconciliation with him, sealed by the Treaty of Valognes on 10 September 1355.
This agreement, too, did not last. Charles befriended and was thought to be trying to influence the Dauphin, and was apparently involved in a botched coup d’état in December 1355 whose purpose appears to have been to replace John II with the Dauphin.
John amended matters by making his son Duke of Normandy, but Charles of Navarre continued to advise the Dauphin how to govern that province.