Howell was born in Llangamarch, Brecknockshire, Wales. Son of Thomas Howell, by a daughter of James David Powell, was born at Bryn, in the parish of Llangammarche, Breckonshire 1588, His father rector perpetual of Llangammarche and also of Abernant in Carmarthenshire. He was the older brother of James Howell, and a descendant of Hywel Dda. He matriculated at Jesus College, Oxford on 20 November 1607, obtaining his BA degree on 20 February 1609, his MA on 9 July 1612 and later obtaining his BD degree in July 1630. After his ordination, he was appointed a royal chaplain by Charles I and was also rector of West Horsley in Surrey, becoming rector of St Stephen Walbrook on 13 April 1635. This appointment provoked a dispute between Charles I, the parishioners of the church and the Grocers' Company because Howell refused to live in the parish. Howell was appointed to a canonry of Windsor in 1636 and the sinecure rectory of Fulham in 1642. He faced difficulties during the English Civil War: although regarded as a "puritanical preacher", he was questioned by the House of Commons on 19 March 1642 over allegations that he had criticized parliament and supported Charles I. Even before that, he had been forced out of his position at St Stephen's Walbrook in 1641 and later forfeited the rectory of West Horsley for non-residence. On the death of Thomas Westfield in 1644, Howell was appointed Bishop of Bristol by Charles I. He was consecrated by Archbishop James Ussher in August 1644, and was the last bishop to be consecrated in England for sixteen years. However, Prince Rupert surrendered Bristol to Fairfax on 10 September 1645 and Howell was ejected. He is not known to have attended the Westminster Assembly and is not named in the List of the Westminster Divines, probably taking the same views of its relevance as Ralph Brownrigg, Bishop of Exeter, who did not attend either. Brownrigg is named however, the brevity of Howell's Bishopric, being the cause of non-naming on the list. His whereabouts thereafter until his death but his will left the lease of a property in Frogmore, Windsor to his ten youngest children, so he may have lived there for a time. His wife died shortly before him in childbirth. He was buried in Bristol Cathedral, his memorial stating Expergiscar.
