Nothing Donatus wrote survives. He is reported to have written on the Holy Spirit in terms his opponents thought subordinationist, and letters of his circulated, but no text has come down. Everything we can say about him comes from two hostile witnesses: Optatus, bishop of Milevis, writing around 365, and Augustine, writing from the 390s, both arguing a case against a living movement.
That shapes the picture in predictable directions. Both report that his followers used his name where they should have used a title, that he asked what the emperor had to do with the church, and that he behaved with the pride of a man who thought himself above other bishops. Whether these are quotations, paraphrases or constructions is not recoverable. The general facts of his career are better attested than his character, because the imperial and conciliar record carries them independently of the polemic.
He was exiled in 347, after the mission of Paul and Macarius turned into an armed suppression, and he died in Gaul around 355 without returning. His people continued to regard him as their bishop in absence. The church he led was still substantial when the Vandals arrived and survived until the Arab conquests, which is a long afterlife for a man of whom no sentence survives that he certainly wrote.