His father, who moved in a short time to Rhyd Loew, and thence to Cae Du in the same district, was a lay officer of the Calvinistic Methodist connection, and Henry showed at an early age a deep interest in religious work.

Resolving to devote himself to the Calvinistic Methodist ministry, he came home to Cae Du in May, and then placed himself for two years under the tuition of Thomas Lloyd of Abergele.

During his stay in Shrewsbury Rees rapidly won a position as one of the foremost preachers of his connection, and from this time until his death was almost always to be heard at the great preaching meetings of the North Wales Association.

After the death of John Elias in 1841 he was for a quarter of a century the recognised leader of the Calvinistic Methodists of North Wales, and had the largest share in forming the policy of the northern association.

As a preacher he had scarcely a rival in the denomination, his sermons being marked by careful preparation, closeness of texture, and purity of diction, coupled with great earnestness and force.