Puritan writer whose Llyfr y Tri Aderyn (1653; “The Book of the Three Birds”) is considered the most important original Welsh work published during the 17th century. One of the most widely read of Welsh classics, the work is in two parts, on the theory of government and on religious liberty. The book is in the form of a discourse conducted among the eagle (Oliver Cromwell, or the secular power), the raven (the Anglicans, or organized religion), and the dove (the Nonconformists, or the followers of the inner light).

Llwyd came from a gentry family and probably received his early education at Wrexham, Denbighshire. In the English Civil Wars he served as a chaplain in the Parliamentary army. He was identified with the first Dissenting church in Wales. His other works include Llythyr ir Cymry Cariadus (1653; “Letter to the Beloved Welsh”). A selection of his works was published by the University of Wales in two volumes (1899, 1905).