Formed in the Baumholder area from replacement center personnel in January 1944 under the command of Generalleutnant Bruno Ortner, its command was transferred to Generalleutnant Wilhelm Falley and moved to the Cotentin peninsula with von der Heydte's 6th Parachute Regiment and 100th Panzer Replacement and Training Battalion, armed with captured French light tanks, attached as part of the German 7th Army.

Placed under the temporary command of Generalmajor Bernard Klosterkemper, It attempted to block the U.S. 4th Infantry Division's advance off Utah Beach.

After the second week of the Allied invasion of Normandy the 91st had suffered so many casualties it was no longer considered combat effective as a unit.

Despite recommendation the unit be dissolved the Army High Command (Oberkommando des Heer, OKH) chose to rebuild it adding replacement battalions and sending it back to the front in early August.

Defending Rennes from Lieutenant General George S. Patton's U.S. Third Army, it again suffered heavy casualties and was reduced to battle group strength.