Born and raised in Carmarthen and the Vale of Glamorgan, Iestyn studied law at Aberystwyth and Cardiff universities. After qualifying in 2005, he worked in private practice in Cardiff, where he went on to become a Partner specialising primarily in employment law. He joined S4C in 2018, leading the legal and business affairs teams. In his role, Iestyn serves as a non-executive director of the Educational Recording Agency (ERA). He has also been a trustee with Colegau Cymru and the charity Tenovus, and continues to serve as a governor at Cardiff and Vale College and Ysgol Garth Olwg. He joined S4C's Senior Leadership Team in January 2025.