Roberts found inspiration in the local community, painting industrial workers and farmers, and domestic scenes of family life. Some of Roberts' most striking works are of Welsh landscapes and he is now widely acknowledged as one of Wales's modern masters. In 1962, Roberts won the Byng-Stamper Prize for landscape painting, judged by Sir Kenneth Clark, for Farm at Cimla which was acquired by the National Museum of Wales. In 1992, he was awarded an honorary Fellowship by University College, Swansea, and in 1994 a retrospective exhibition of his work was the centrepiece of the arts exhibit at the National Eisteddfod of Wales. In 1998, the National Library of Wales accepted a donation of 600 drawings from Roberts.