It is known that he was a senior knight in good standing in 1245 when he assumed the position of interim Grand Master during the captivity of Guillaume de Chateauneuf.
[5] De Ronay served in as interim Grand Master through the Seventh Crusade, led by Louis IX of France.
On 17–18 October 1244, the Crusader troops, which included approximately 1,000 cavalry and 6,000 foot soldiers, engaged in the Battle of La Forbie, were decisively defeated by Baibars.
Only 280 horsemen (including 33 Templars, 27 Hospitallers, 3 Teutonics and the Lord of Tyre, Philip of Montfort) and a thousand soldiers survived the defeat which marked the end of Christian military power in the Holy Land.
In the fall of 1245, it was the capture of Damascus by Egyptian troops aided by the Khwarezmians that which put Egypt and Syria in the hands of as-Salih Ayyub.
Guillaume de Chateauneuf was released eight months later, on 17 October 1250 upon payment of his ransom, and thence returned to the leadership of the Hospitallers.