Meisinger was born in Munich, the son of Josef and Berta Meisinger; he enlisted on 23 December 1916 and served during World War I in the 230th Minenwerfer Company (a type of short-range mortar), 22nd Bavarian Pioneer Battalion in the 30th Bavarian Reserve Division. After being wounded in battle he was awarded the Iron Cross and the Bavarian Military Merit Cross. On 18 January 1919 he attained the rank of Vizefeldwebel (senior sergeant), and on 19 April 1919 he entered the Freikorps under Franz Ritter von Epp, with whom he fought against the Soviet Republic of Bavaria.