Breadner obtained his pilot's certificate at Wright Flying School and was commissioned in the British Royal Naval Air Service on December 28, 1915.

On the morning of the 11th April, 1917, he destroyed a hostile machine which fell in flames, brought down another in a spinning nose dive with one wing folded up, and forced a third to land.Squadron Commander Lloyd Breadner and 3 (Naval) Squadron were posted to RAF Walmer during the Winter of 1917/1918 .

He was commissioned promoted to Squadron Leader in 1920 and transferred to the Royal Canadian Air Force (RCAF) on its formation in 1924.

Breadner was promoted on his retirement on November 25, 1945, to Air Chief Marshal, the first Canadian to hold this rank.

On November 30, 1944, while he was Chief of Air Staff, his son, Flying Officer Donald Lloyd Breadner, was killed after an air gunnery exercise, while flying a de Havilland Mosquito from RCAF Station Debert, in Nova Scotia.