In the meantime in 1263 Mindaugas of Lithuania was murdered. In the chaos that followed Mindaugas' assassination, the lands of the Grand Duchy were in disarray, with both local and foreign rulers struggling for power. Shvarn gave his support to Vaišvilkas, one of Mindaugas' sons and his brother-in-law. Together they managed to depose Treniota and expel Dovmont all the way to Pskov. After Vaišvilkas returned to monastic life in 1267, Shvarn became the new Grand Duke. No details are known about Shvarn's rule over Lithuania and he probably did not gain a strong foothold in that country. However, he was apparently fairly successful in expanding his borders. Following successful military campaigns, in 1267 he defeated his brother Mstislav in the battle of the Yaselda River and captured Turov and Pinsk. He then campaigned against the Volga Tatars and defeated khan Balaklay in the battle of Kojdanow (modern Dzyarzhynsk, Belarus), which allowed Shvarn to capture the towns of Mozyr, Chernigov, Karachev and Starodub. The struggle for power within Lithuania however continued. Before a clear winner could emerge, Shvarm died in Kholm (nowadays Chełm, Poland) some time between 1269 and 1271. He was buried in an Orthodox Cathedral that once stood on a place now occupied by the Basilica of the Birth of the Virgin Mary. After his death most of his lands reverted to Lithuania and came under the control of Traidenis, a noble from Aukštaitija.