He took over from Armengol de Aspa to become Grand Master at an unknown date, but generally considered to be between July 1189 and 25 March 1190.

The Templars formed the vanguard, the Breton and Angevin knights the first group, in the second the Poitevins under the orders of Guy de Lusignan, the third the Normans and the English and at the rear, the Hospitallers.

[5] Richard had previously ordered no direct engagement with the enemy on the march to capture Jaffa during the Battle of Arsuf.

Situated at the rear of the military column, Garnier's Hospitallers were under heavy pressure by the Muslims.

They were constantly harassed with arrows and small scale hit-and-run attacks in an attempt to disrupt and lure the crusader column into full battle.

According to the 13th-century manuscript Itinerarium Regis Ricardi, Garnier was near breaking point and rode forward in person to try to persuade Richard to attack: My lord the king, we are violently pressed by the enemy, and are in danger of eternal infamy, as if we did not dare to return their blows; we are each of us losing our horses one after another, and why should we bear with them any further?

When the pressure increased, the Grand Master and one other knight, Baldwin de Carreo, charged the Saracens.

[7][8] Actor Donald Sumpter portrays Garnier de Nablus in the 2008 BBC TV docudrama series Heroes and Villains, which features a reenactment of the Battle of Arsuf.