[3] His small publishing house, Modern Welsh Publications Ltd, was established in 1963 and from 1963 to 1968 it operated from Abercynon in the Cynon Valley of South Wales.

The farm was in the ownership of his grandfather David Benjamin, and after his death in 1944, he and his parents moved to Llanddewi Brefi, where he attended the local primary school.

His friends from seconday school included John Davies, Dr Lewis Evans of Alliance & Leicester and others later in academia and business.

In his proactive approach, he became a prominent member of the debating society called "Cymdeithas Grug Y Gors" (named after the local marshland of Cors Caron).

During this time, he and W. I. Cynwyl Williams were awarded the Byrsgyll y Cymro (Best debating team in universities and colleges of Wales).

This was well received and attracted articles from well-known Labour politicians such as his widow, Jenny Lee, and the Transport and General Workers' Union organiser, Huw T. Edwards.

When the disaster of 21 October 1966 occurred,[6] where 116 children and 28 adults died under the collapse of a coal tip, he and other ministers were involved in comforting the families and organising the local Aberfan committee.

In 1968 he moved to Liverpool with his wife, mother-in-law and son Dafydd, as minister at Bethel chapel in Heathfield Road of the Presbyterian Church in Wales.

His role involved a great deal of travel including five times to the USA, as well as to China, Russia, Malaysia and several European countries as well as arranging 22 pilgrimages to Israel.

Rees and his wife were introduced to Queen Elizabeth II at the opening of the Kingsway Tunnel between Liverpool and Wallasey.

Local and Welsh media invited him to contribute to programmes including Songs of Praise and Radio Merseyside:[7] From the valleys I came.

He kept alive the traditions of the Welsh and established societies that would be assistance, such as the Merseyside Chair Eisteddfod, the Council of Welsh Chapels on Merseyside, a charity with his son Hefin Rees (Generating Hope in Action[8]), the University of Wales Guild of Graduates[9] (Liverpool branch), and the local community newspaper Yr Angor/The Anchor,[10] which he edited from 1979.

He was involved as a tutor, examiner, and a board member[11][12] for the Greenwich School of Theology,[13] as well as at the North-West University,South Africa[14] where he was made a professor.

This campaigning for peace and justice brought him into friendship with Reverend Lord Donald Soper, Earl Bertramd Russel, Daniel Berrigan, Gwynfor Evans MP, and Monsignor Bruce Kent.

In a review in the monthly magazine Barn the Reverend Alwyn Roberts praised the title for bringing the contribution of Gandhi to a new generation of readers.

The Welsh addition appeared in 1979, and gained him the Ellis Griffith Prize of the University of Wales, for the best academic book of that year.

Dr. Rees has used the letters which Thomas' grandson Saunders Lewis had preserved to give a profound and interesting account of one of the most outstanding authorities on the history and development of Welsh preaching.

This biography will introduce Dr. Owen Thomas to a wider circle of scholars who have not been able to appreciate his contribution as all his published works were in the Welsh language."

He delivered the prestigious Davies Lecture on John Calvin and the Connexion at the General Assembly of his denomination in Lampeter in 2008.