As part of the French intervention in the Irish Rebellion of 1798, Schwarz sailed there with a contingent of troops but was captured on 12 October 1798 at the Battle of Tory Island. Schwarz was promoted chef de brigade (colonel) of the 5th Hussar Regiment on 3 September 1799. In the 1800 spring campaign in southern Germany, his regiment was assigned to General of Division Antoine Richepanse's division. The 5th Hussars fought at the Battle of Messkirch on 4 and 5 May, at the Battle of Biberach on 9 May, and at Kirchberg an der Iller.