In 1387 battle with the Teutonic Knights Lengvenis commanded one of Lithuanian formations. In 1389–1392 he was appointed by his brother Władysław II Jagiełło, Grand Duke of Lithuania and King of Poland, as regent of Great Novgorod. He was baptized in the Orthodox rite as Simon and received the title of Prince of Great Novgorod.
In 1387 battle with the Teutonic Knights, Lengvenis commanded one of Lithuanian formations. In 1389–1392, he served as regent of Great Novgorod under his brother Władysław II Jagiełło, Grand Duke of Lithuania and King of Poland. He was baptized in the Orthodox rite as Simon and given the title of Prince of Great Novgorod.