The son of Hugh Witherow, a farmer at Aughlish, near Dungiven, County Londonderry, and his wife Elizabeth Martin, he was born at Ballycastle on 29 May 1824.
He received his early education at Ralliagh church school, and then studied with James Bryce.
In 1839 he entered the collegiate department of the Academical Institution, and here, with the exception of a session at Edinburgh, all his college days were spent.
In 1865, on the opening of Magee College, Londonderry, he was appointed by the General Assembly as Professor of Church History and Pastoral Theology.
[3] In 1878 Witherow was elected moderator of the Irish General Assembly, and in 1884 as a senator of the Royal University of Ireland.