Daniel James came from Treboeth in Swansea. He lost his father at an early age, later becoming a puddler at Morriston ironworks, and afterwards worked at Landore tinplate works.
He began to write verse and assumed the bardic name Gwyrosydd (meaning "Truth will Stand" or "Man of Gower"). He later found work in Tredegar, Dowlais Ironworks, Blaengarw, and Mountain Ash, Rhondda Cynon Taff, where he spent 20 years.
Much of his verse appeared in periodicals and newspapers, but collections were also published. Calon Lân is easily his most popular hymn, and regularly tops the lists of favourite Welsh hymns. He is thought to have written the words while he lived at Blaengarw, and the local council is to open a new park (Parc Calon Lân) in his honour in 2008.