He married Sophia Olelkovich, princess of Slutsk of Lithuanian origin[1] in 1471 (died February 6, 1483), then a granddaughter of Casimir IV Jagiellon, and eventually lost the title when Ivan III of Moscow conquered Tver in 1485.

[2] The prominent Russian historian Nikolay Karamzin described the Principality of Tver in the middle of the 15th century as a state, equal to Moscow in glory and rights.

In 1463, Ivan III conquered the Principality of Yaroslavl, in 1478 he annexed Novgorod, so Lithuania remained the only possible ally of Tver against Moscow.

In 1485, Mikhail III "acknowledged himself as a lesser brother" and signed a peace treaty, sworn to fight on side of Moscow in any wars.

Mikhail decided to flee to Lithuania, but the messenger with his private letter to king Kazimir was stopped by Ivan's people.