In the Seven Years' War, his brilliant conduct at the churchyard of Leuthen and at Hochkirch won him promotion to major. In 1760, in the almost lost Battle of Torgau, Möllendorf was captured by the Austrians, but released in 1761, and was made major general later in the year. He received an Order of Merit for his exertions. At the Battle of Burkersdorf Möllendorf commanded a brigade that participated in the successful assault of the fortified Austrian positions.