Heylyn was the son of David Heylyn of the historical Heylyn family of Pentreheylin in Powys, Wales.
Heylyn married Jane Slaughter, daughter of Charles Slaughter, a Blackwell Hall factor and had four sons and two daughters.
Very few of his engravings exist, notably a portrait of Thomas Cromwell, Earl of Essex, published by P. Stent in 1658, a good work; a portrait of his master, Faithorne, from a drawing by himself; a copy of J. Payne's portrait of Paracelsus; ‘Dr. Michael,’ after Guido Reni; and the frontispiece to P. Heylyn's ‘Cosmography,’ published in 1669.
Heylyn supported with Thomas Myddelton publication of the Welsh quarto Bible of 1630, which was bound with the Welsh Prayer Book and the Edmund Prys translation of the Psalter.