Möllendorf was born in Lindenberg (Prignitz), now a part of Wittenberge, in the Margraviate of Brandenburg. He began his career as a page of King Frederick the Great in 1740. The outbreak of the Silesian Wars gave him his first opportunity of seeing active service, and the end of the second war saw him a captain, promoted for bravery at Soor (1746). He passed the remainder of his life in retirement. He died in 1816 in Potsdam.