Donellan, Nehemias (Daniel, Nehemiah; Ó Domhnalláin, Fearganainm) (d. 1609), protestant archbishop of Tuam and Irish-language scholar, was born in Co. Galway, son of Maoileachlainn Ó Domhnalláin and his wife Sisile Ní Cheallaigh. The O'Donnellans were a well known and learned family frequently mentioned in the annals. He enrolled at Cambridge University on 13 January 1579/80 under the name Nehemiah Daniel and attended both King's College and Catherine Hall, receiving his BA in 1582.
He returned to Ireland and was residing in the diocese of Kilkenny when he was mentioned in a 1591 document on the state of religion in Connacht as one of the few protestants in the country who could preach the gospel in the Irish language. He later became coadjutor to William O'Mullally, archbishop of Tuam (1572–95), before being appointed his successor in 1595. This appointment was due both to the translation work he had done for the church and to his ability to communicate with the people in their own language, as the writ directing his appointment mentions. In addition to his bishopric he held by dispensation the rectory of Kilmore, Co. Kilkenny, and the vicarages of Castledoagh in the diocese of Ossory, and of Donard in the diocese of Dublin.
He was one of the translators of the New Testament for which Elizabeth I early in her reign had provided funds. The translation was completed by William Daniel (qv) and published in Dublin (1603) under the title Tiomna nvadh ar dTighearna agvs ar Slanaightheora Iosa Criosd, and was the means by which it was expected the Roman catholic church in Ireland would be destroyed. In addition, Donellan did much of the translation of the Book of Common Prayer, which William Daniel published (1608) as Leabhar na n-vrnaightheadh gcomhchoidchiond.
He married (date unknown) Elizabeth, daughter of Nicolas O'Donnell. One of their five sons, James (qv), was knighted, and became lord chief justice of the common pleas in Ireland. Donellan died in Tuam in 1609, shortly after resigning his see, and was buried in the cathedral there.