The Monk Gennady, in the world Gregory, came from the family of the Russian-Lithuanian boyars John and Elena; he was born in the city of Mogilev. Since childhood, the boy loved to visit the temple of God, and finally, deciding to enter one of the monasteries in the Russian land, he secretly left his parents' home, exchanged rich clothes from beggars for rags and reached Moscow in this form. Here he met his future spiritual friend named Theodore, who also aspired to monastic feats. Unable to find refuge in the Moscow region, the ascetics went to the Novgorod land.; Here they met with the Monk Alexander Svirsky, who blessed his friends to go to the Vologda forests to visit the Monk Cornelius Komelsky.

Saint Cornelius predicted to Theodore that his fate would be a worldly life (indeed, Theodore soon returned to Moscow, had a large family, and lived to a ripe old age), and Gregory left in his monastery, where, after a long time of novitiate, he took the veil with the name Gennady.

Under the spiritual guidance of the elder, the novice monk zealously worked in the monastic field, thus arousing the envious indignation of the monastery's brethren. Finally, the monks' indignation fell on Saint Cornelius himself, and he and his disciple had to leave the monastery. Having moved to Surskoye Lake (60 versts from the Komel Monastery), the ascetics built cells there, dug four ponds, and engaged in farming. However, Grand Duke John Vasilyevich (the future Tsar John the Terrible), having visited the Komel monastery and not finding St. Cornelius there, ordered the holy elder to be returned to his former place, and St. Gennady remained in charge of the newly created monastery, where the brethren had already begun to gather.

For his companions, the Monk Gennady was a true example of meekness, humility and diligence: he chopped wood and carried it to the cells at night, worked in the cook and bakery, washed hair shirts for the brethren. He was particularly successful in the feats of prayer and fasting; even during his lifetime, the Lord honored the monk with the gift of perspicacity and miracle-working. So, one day, while in Moscow, Saint Gennady predicted to the daughter of the boyar Juliania Zakharina the royal crown – which soon came true: Anastasia Zakharina became the wife of Tsar John the Terrible.

In 1565, the monk peacefully reposed and was buried in the Spassky Monastery he had created. In 1646, the Church glorified him as an all-Russian venerated saint, and the incorruptible relics of the monk (discovered during the construction of a new stone church during the time of Tsar Mikhail Feodorovich) remained to rest under a bushel in his monastery, in a special chapel of the cathedral church in the name of the Transfiguration of the Lord.

After the events of 1917, the Spaso-Gennadiev Monastery was abolished, the relics were blasphemously opened on September 28, 1920. Currently, this monastery (located within the Yaroslavl diocese, on the border of the Kostroma and Yaroslavl regions, near the city of Lyubim) is still in disrepair. Since 1983, St. Gennady's Memorial Day has also become the day of celebration of the Kostroma Saints Cathedral. The Trinity Church in the village of Sandogora (Kostroma Diocese), located next to the Spaso-Gennadiev Monastery, has long maintained the pious tradition of celebrating the annual local celebration of St. Gennady on September 1.