Sainted Theodosii (Feodosii), Archbishop of Chernigov, was born at the beginning of the decade of the thirties of the XVII Century in Podol'sk governance. He was descended from an old court-nobility lineage, the Polonitsky-Uglitsky's. His parents were the priest Nikita and Maria. The piety prevailing within the family of the future saint contributed greatly to the spiritual growth of the boy. From childhood he distinguished himself with his gentleness and disposition towards prayer. The innate abilities of the youth came to light in the Kievo-Bratsk college at the Kiev Theophany monastery. This was a time of an extensive flourishing of the college (the end of the 1640's), when its rectors were the archimandrite Innokentii (Gizel'), and later the hegumen and afterwards archbishop of Chernigov, Lazar (Baranovich). Among its instructors were: the priestmonk Epiphanii (Slavinetsky), the priestmonk Arsenii (Satanovsky), the Belorus bishop Theodosii (Baevsky), the hegumen Theodosii (Saphonovich) and Meletii Dzik – all these were indeed men of enlightenment for those times. The comrades of Saint Theodosii at the college were themselves to become future outstanding pastors: Simeon Polotsky, Ioannikii Golyatovsky, Antonii Radivillovsky, Varlaam Yasninsky. The Kievo-Bratsk Theophany school was at this time the chief centre in the struggle of Orthodoxy against the assaults of Catholic clergy, and Jesuits and Uniates.
The vocation of Saint Theodosii to the monastic life ultimately formed during his years of study: he devoted all his free time to prayer, meditation on God and the reading of Sacred Scripture.
It might be surmised, that the saint did not finish the full course of the college studies, since the school ceased its activity for several years following the devastating of Podolia by the Poles. The saint all his life had deep regard for the Kievo-Bratsk monastery that had educated him. In the Synodikon of the Kievo-Vydubitsk monastery is the following remark about Saint Theodosii: "He was a man of fine intellect and generous to the Kiev Bratsk monastery".
Upon receiving his education, the future hierarch accepted monastic tonsure at the Kievo-Pechersk Lavra with the name Theodosii, in honour of the Monk Theodosii (Feodosii) of Pechersk (Comm. 3 May) (worldly name unknown).
The Kiev metropolitan Dionysii (Balaban) made him archdeacon of the Kiev Sophia cathedral, and then appointed him administrator of the metropolitan cathedral house. But soon he left Kiev and resettled at the distant Krutitsk monastery (in Chernigov diocese), near the locale Baturino, which was famed for its strict monastic life. He was consecrated there to the dignity of priestmonk. In the year 1662 Saint Theodosii was appointed hegumen of the Korsunsk monastery in Kiev diocese, and in the year 1664 – was made head of the ancient Kievo-Vydubitsk monastery. This monastery shortly before had fallen into the hands of the Uniates and was in complete ruin. But thanks to the energy and initiative of Saint Theodosii, the Vydubitsk Mikhailovsk monastery was quickly restored. He concerned himself in particular about the order of churchly property. He formed an excellent choir, which was famed not only in Little Russia, but also in Moscow, where Saint Theodosii in 1685 sent his singers. And concerning himself over the spiritual growth of the monastery inhabitants, being himself a strict ascetic, in 1680 the holy hegumen made on the island of Mikhailovschina, not far from the monastery, a small skete-monastery for brethren wishing solitude. He appointed there to organise and administrate it one of the most zealous monks of his monastery – the priestmonk Job (Opalinsky).
In his role as hegumen of the Kievo-Vydubitsk monastery, Saint Theodosii had to live through some quite difficult days. He was accused together with other hegumens by Methodii, bishop of Mstislavsk and Orshansk, of betraying the Russian governance in a supposed correspondence with those treasonous to Russia. On 20 September 1668 Saint Theodosii had occasion to give an explanation in the matter. And on 17 November 1668 the slander unraveled, and Saint Theodosii together with the other hegumens received a pardon. His Grace Lazar (Baranovich) esteemed the high spiritual qualities of Saint Theodosii and befriended him. He called him "a sheep of the flock of Christ, teaching by humility", and he prophetically expressed the wish, that the name of Saint Theodosii might be inscribed in Heaven. When His Grace Lazar in 1689 became locum tenens of the Kiev metropolitan see, he appointed Saint Theodosii as his vicar in Kiev, while he himself remained at Chernigov. In his capacity as vicar of the locum tenens of the Kiev metropolitan see, Saint Theodosii had an active role in many a churchly event. In 1685 he participated with the right of a decisive vote in the selection of bishop Gedeon (Chetverinsky) as metropolitan of Kiev, and he was sent to Moscow with news of this event together with the Pereyaslavl' hegumen Ieronim (Jerome) (Dubin). In Moscow both representatives were received with honour and esteem. And indeed, the result of this delegation was the re-uniting of the Kiev metropolitan see with the Russian Orthodox Church.
In 1688 Saint Theodosii was appointed archimandrite of the Chernigov Eletsk monastery, replacing the deceased archimandrite Ioannikii (Golyatovsky). And from the time all the activity of the saint transferred over from Kiev to Chernigov. This appointment comprised primarily, in accord with the wishes of His Grace Lazar, that Saint Theodosii should spare no little toil over putting back the Eletsk monastery in good order, since this monastery had not yet been set aright after the expulsion of the Jesuits and Dominicans, and it was very much in bad shape and disorder. Through the efforts of Saint Theodosii, good results were achieved over the course of two or three years, which then fully guaranteed its existence. The saint in his new position also rendered all kinds of assistance to His Grace Lazar in all kinds of important matters. He participated in composing a conciliar reply to the Moscow Patriarch Ioakim in response to his letters questioning the attitude of the Kiev metropolitan see to the Council of Florence, and its judgement on the question of the transformation of the Holy Gifts as accepted by this Florentine Council. When the Patriarch proved to be unsatisfied by these answers, there was dispatched to him at the beginning of 1689 the Baturinsk hegumen Saint Dimitrii (Tuptalo) (the future metropolitan of Rostov). Saint Theodosii journeyed with him in the capacity of representative of His Grace Lazar. He was entrusted to present the Patriarch a letter of reply and to clear up the misunderstandings. On 11 September 1692 Saint Theodosii was solemnly ordained an archbishop in the Uspenie (Dormition) cathdral of the Moscow Kremlin.
Little in the way of an account of the governance by Saint Theodosii of the Chernigov diocese has been preserved. The saint directed special attention to the rousing and increase in the flock of a true Christian piety. With this end in mind he concerned himself with the upkeep of the old and the building of new monasteries and churches. At the very beginning of his episcopate, with his blessing, there was established the Pecheniksk women's monastery, and he himself consecrated the monastery church in honour of the Uspenie (Dormition) of the MostHoly Mother of God. In 1694, with his blessing, there was founded the Liubetsk skete-monastery, 2 versts from Liubech. In 1694 also the saint consecrated at the Domnitsk men's monastery a temple in honour of the Nativity of the MostHoly Mother of God. And in the Summer of 1695 he consecrated a majestic temple in honour of the MostHoly Mother of God, built on the summit of Boldinsk Hill, near the ancient Il'insk monastery. Under Saint Theodosii may be noted an especial enthusiasm and strengthening of monasticism in the Chernigov diocese. The saint also devoted great attention to the clergy, and he was a strict questioner in the selection of candidates for priesthood. He gave especial patronage to the Chernigov clergy school, he invited learned monks from Kiev, among whom was Saint John (Maksimovich), the future metropolitan of Tobol'sk, but likewise an helper and successor of Saint Theodosii in organising the Chernigov clergy school. Strict uprightness in regard to clergy and flock, deep compassion, concern and Christian love of peace were distinguishing features in the activity of Saint Theodosii. To him often turned not only the Orthodox for aid and advice, but even persons of other confessions.
But Saint Theodosii could not long sustain the Chernigov flock. Sensing the approach of death, he summoned to him the administrator of the Bryansk Svensk monastery, Saint John (Maksimovich), and elevated him from priestmonk to archimandrite of the Chernigov Eletsk monastery. In this new archimandrite he prepared beforehand his successor. On 6 February 1696 Sainted Theodosii died and was buried in the Chernigov Borisoglebsk cathedral church, beyond the right kleros-choir, in a special crypt made for this. His successor Sainted John (Maksimovich) later built over his grave a brick arch with an eulogistic inscription in verse, in gratitude for a miraculous healing from a grievous illness. The special granting of grace to which Saint Theodosii attained, is testified to by his ascetic life and his hidden help to all, who recourse to him in prayer.
The glorification of Saint Theodosii occurred on 9 September 1896.