[citation needed] Grenfell was educated at Penyrheol Board Elementary School until 1893, when, at the age of 12, he was forced to start working as a coal miner underground himself.

Grenfell taught at a number of evening classes himself from 1907 to 1911, and was named a miners' agent in 1916 for the Western Region of the South Wales Area of the Coalminer's Federation upon the death of his predecessor, William Morgan.

[2] Grenfell continued to work underground until 1916, when he was appointed the miners agent for the Western Region of the South Wales Area.

"[3] He acted as chairman of the Welsh Parliamentary Labour Party, and in Winston Churchill's coalition government during World War II he served as Secretary for Mines at the Board of Trade (1940–45), in which capacity he argued for the nationalisation of the coal industry, and reiterated the call in his 1947 book, Coal.

In 1953 Grenfell became the first Labour politician to hold the title "Father of the House", as the longest continual serving Parliamentarian.

"[7] Grenfell held office in many local bodies, and was made an Honorary Freeman of Swansea for his contribution to public service.

His brother, William John Grenfell, was for a number of years a member of Llwchwr Urban District Council, representing the Pontybrenin ward.