I. The following short biography is taken from the work Ketaba de Nakfuta:
This translation is reproduced from the introduction to A.J. Wensinck's "Mystic Treatises by Isaac of Nineveh" (Amsterdam, 1923, p. XVIII). The footnote below is added by the editor of Isaacthesyrian.com.
"On the holy Maar Isaac, bishop of Ninive, who resigned his episcopal office and wrote books on the behaviour of solitaries.
He was ordained a bishop of Ninive by Mar George the Katholikos, in the monastery of Bet 'Abe. After he had held the pastoral staff at Ninive for five months, as the successor of bishop Moses, he resigned his episcopal office, for a reason which God knows, and went away to live in the mountains. And after the chair had been vacant for this time, the blessed Sabr Isho' was ordained as his successor, who also left his episcopal office and became an anchorite in the days of Hanan Isho' the Katholikos, and departed this world in the monastery of Mar Shehin in Kurdistan.
When Isaac left the chair of Ninive, he ascended the mountain of Matut which surrounds Bet Huzaje and lived in solitude among the anchorites who were there.
Afterwards he went to the monastery of Rabban Shabur and became exceedingly well acquainted with the divine writings; at last he lost his eyesight through his reading and asceticism. He penetrated deeply into the divine mysteries and wrote books on the divine behaviour of solitaries. He said three things which were not accepted by the community. Daniel, the bishop of Bet Garmaia, was scandalized at him on account of these things which he said. In high age he departed this temporary life; his corpse was interred in the monastery of Shabur. He was born in Bet Katraye; I think that envy was aroused against him by people of the country even as it was against Joseph Hazayya and John of Apamea and John de Daliyateh .
1. John de Daliyateh is more commonly referred to as John of Dalyatha or John Saba, the "Elder".
II. Another ancient biographical text (which appeared in the Studia Syriaca) was also translated by A.J. Wensinck:
(This translation is reproduced from the introduction to A.J. Wensinck's "Mystic Treatises by Isaac of Nineveh" (Amsterdam, 1923, p. XVIII-XIX).)
This Mar Isaac of Ninive was born in Bet Katraye beneath India. When he had become excercised in the writings of the Church and their commentaries he became a monk and a teacher in his country. And when Mar George the Katholikos went to his own country, he took Isaac with him to Bet Aramaye, because he was a relative of Mar Gabriel Katraya, the commentator of the church. Mar Isaac was ordained bishop of Ninive in the monastery of Bet 'Abe. But because of his keen mind and his zeal, he could endure the pastoral function for five months only. Then he returned to his solitude, after he asked the permission of Papa, who dismissed him and ordered him to go and live in solitude in the Mountain of Bet Huzaye with the monks who dwelt there. At last he became blind, so that the brethren wrote down his doctrine. They gave him the surname of the second Didymus, because he was placid and kind and humble, and his speech was meek. He ate only three loafs of bread a week, with small vegetables; he never tasted what was cooked. He wrote five volumes which are extant till now [full of] sweet doctrine. This is attested by Mar Jozadak in the letter which he wrote to his pupil Bushir, to the monastery of Mar Shabur, saying: I thank the Lord because of your diligence which has sent me the doctrine of Mar Isaac of Ninive. I know that you have acquired in your life the keys of the kingdom, because you have filled our monastery with doctrine full of life. For we confess that we are pupils of Mar Isaac the bishop of Ninive. So he writes in his letter. And in the end he says, even as John the Bishop: the writings of Mar Isaac have been of great support and strengthening power to me. When he had grown old had reached a high age, he departed unto our Lord. And he was buried in the monastery of Mar Shabur.
Links to several biographical sketches on Saint Isaac can be found in the links section.