He descended from a notable but an impoverished boyar family from Rostov. Before taking the monastic vows he was named Varfolomey Kirillovich. As a young person yet Sergius of Radonezh became the head of the Trinity Monastery cofounded by him and Brother Stephane.

Living in a very modest way, Sergius did not look much different from a peasant and did not try to avoid farming work. In spite of that, he soon became one of the spiritual advisors of young Prince Dmitry (subsequently known as Dmitry Donskoy; Sergius later became the godfather of his children). The place of the prince’s confessor opened him way to political activity. In 1374 Sergius took part in a big congress of Russian princes in Pereslavl, where they agreed on a joint battle against Mamay, and later blessed Dmitry Donskoy for this fight. In 1378-1379 he dealt with organizational matters of the Russian church and monastic life. Sergius introduced the cenobitic monasticism charter, which substituted the previous custom of monks’ separate stay. He and his disciples carried out enormous work on organization and construction of Russian monasteries.

In the 80s Sergius of Radonezh settled conflicts between Moscow and other principalities (Ryazan, Nizhny Novgorod). Thus, contemporaries highly appreciated him.