Zappas became a member of the Greek patriotic organization Filiki Eteria and joined his compatriots when the Greek War of Independence broke out in 1821. During this period, Zappas reached the rank of Major in the revolutionary army and became a personal friend of the Souliot captain, Markos Botsaris. After Botsaris's death in 1823, Zappas served under various military commanders of the independence struggle, such as Dimitrios Panourgias, Kitsos Tzavelas, and Michail Spyromilios. He participated in several major conflicts, such as the siege of Souli, the first siege of Missolonghi and the Battle of Peta. In his later correspondence with a Greek official, he claimed that he was wounded five times during the war.