He was 26 years old, and a lieutenant in the 51st Battalion, Australian Imperial Force during the First World War when the following deed took place during the Second Battle of Villers-Bretonneux for which he was awarded the VC.
War Office, 11th July, 1918.
His Majesty the KING has been graciously pleased to approve of the award of the Victoria Cross to the undermentioned Officers and Non-Commissioned Officer: —
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On 24/25 April 1918 at Villers-Bretonneux, France, Lieutenant Sadlier's platoon had to advance through a wood where a strong enemy machine-gun post was causing casualties and preventing the advance. Although he was himself wounded, Lieutenant Sadlier at once collected his bombing section and led them against the machine-guns, killing the crews and capturing two of the guns. By this time his party were all casualties and alone he attacked a third enemy machine-gun with his revolver, killing the crew and taking the gun. In doing so, he was again wounded.The very gallant conduct of this officer was the means of clearing the flank, and allowing the battalion to move forward, thereby saving a most critical situation. His coolness and utter disregard of danger inspired all.