In the following year he became lieutenant-general and in 1739 general of infantry. During the life-time of King Frederick William, Schwerin was also employed in much administrative work. Frederick the Great, on his accession, promoted Schwerin to the rank of general field marshal and made him a count. Early in the First Silesian War, he justified his sovereign's choice by his brilliant leadership at the Battle of Mollwitz (10 April 1741), which, when he had persuaded the king to leave the battlefield explaining that he may be captured as a defeat was likely, converted a doubtful battle into a victory which decided for the time being the fate of Silesia.