In Paris he became advocate to the parlement (1347); then John II appointed him master of requests, and in 1351, a year during which he received many other honors, he became bishop of Laon.
At the opening of 1354 he was sent with the cardinal of Boulogne, Peter I, Duke of Bourbon, and Jean VI, count of Vendôme, to Mantes to treat with Charles the Bad, king of Navarre, who had caused the constable, Charles d'Espagne, to be assassinated, and from this time dates his connection with this king.
At the meeting of the estates which opened in Paris in October 1356 le Coq played a leading role and was one of the most outspoken of the orators, especially when petitions were presented to the dauphin Charles, denouncing the bad government of the realm and demanding the banishment of the royal councillors.
The king of Navarre had succeeded in escaping from prison and had entered Paris, where his party was in the ascendant; and Robert le Coq became the most powerful person in his council.
He ran great danger at the estates of Compiègne in May 1358, where his dismissal was demanded, and he had to flee to Saint-Denis, where Charles the Bad and Étienne Marcel came to find him.