Rhys attended Ysgol Gyfun Gymraeg Glantaf in Llandaff North, before reading law at the University of Oxford.

Later, ab Owen stood in the 2021 Senedd election as a Plaid Cymru candidate for Cardiff West, competing against the incumbent MS and First Minister Mark Drakeford (Welsh Labour).

[9] He also is a member of cross-party groups on beer and pubs, dementia, digital rights and democracy, faith, lung health, policing, Public and Commercial Services Union (the Senedd's relationship with it) and rented housing and leasehold properties.

[9] On 8 November 2022, ab Owen was suspended from Plaid Cymru, pending an investigation by the Senedd's standards watchdog over an alleged breach of the code of conduct.

He lists his recreations as "Welsh history, choir, family, chapel" and is a member of the Ifor Bach club in Cardiff.