Since the late 1420s, Jonah had been living in the Simonov Monastery in Moscow and was close to Metropolitan Photius, who make him Bishop of Ryazan and Murom. After Photius's death in 1431, Grand Prince Vasili II nominated Jonas for the post of Metropolitan, but the Uniate Patriarch Joseph II chose Isidore to become the Metropolitan of Kiev and All Rus'.
After the death of Photios in 1431, Jonah was chosen by the grand prince and the council of bishops as the new Metropolitan of Kiev and all Rus' at the end of 1432. However, due to internal strifes in Muscovy, he did not hurry to Constantinople to receive his ordination and did not decide to go to Constantinople until the middle of 1435. Meanwhile, at the request of the Lithuanian Grand Duke Švitrigaila, bishop Gerasim of Smolensk [ru] was appointed Metropolitan of Kiev and all Rus', but the latter did not come to Moscow and remained Metropolitan only in Lithuania. Soon, Švitrigaila suspected Gerasim of treason and executed him in 1435.[3][4]
When Jonah finally arrived to Constantinople in 1436, the Ecumenical Patriarch had already chosen the Greek bishop Isidore and appointed the latter as the new Metropolitan of Kiev and All Rus'. Isidore came to Moscow in 1437 and made a good impression there with his diplomatic skills and knowledge of the Slavonic language. However, only 5 months later, in September 1437, he left Moscow to participate to the Council of Florence, where the unification of the Churches of Rome and Constantinople should be adopted.
After Isidore had been condemned and deposed by Vasily II and his bishops in Moscow in 1441, for his attempts to implement the decision on the Union of the Eastern and Western (Roman) Churches agreed upon at the Council of Florence-Ferrara, the metropolitan throne sat vacant for seven years.