In 1372, the Navarrese ranks began to swell through the recruiting techniques of Enguerrand VII de Coucy, who was hired to form a force of 500 lances and 500 mounted archers, mostly from Gascony.
The Navarrese entered Morea in the spring or early summer of 1378, some coming at the invitation of Gaucher of La Bastide, the Hospitaller prior of Toulouse and commandant in the Principality of Achaea and others probably at the bequest of Nerio I Acciaioli.
Gaucher hired Mahiot and the remnant of the company for eight months during the captivity of Grand Master Juan Fernández de Heredia.
In 1379, Urtubia with a large force invaded Boeotia and sacked Thebes, then under the control of the Catalan Company, with the assistance of the archbishop of the city, Simon Atumano.
When James died in 1383, the Navarrese were the reigning power in Frankish Greece, and it fell to them the responsibility of reorganising the state and securing a new prince.
While the Navarrese refused to recognise the heirs of James without proof, which was too costly to provide, they remained in power in Achaea and were licensed by the barons of the realm to negotiate the treaty of 26 July 1387 with the Republic of Venice.