Seiriol is a musical theatremaker who trained at the London International School of Performing Arts. He has made shows with companies like Punchdrunk, You Need Me, Gideon Reeling and Beady Eye. He was half of the cult time-travelling knees-up variety act Underbling and Vow, and writes songs with the dark glam, Weimar-fabulous band Temper Temper.
 
His first full-length play Moon River, an unsettling comedy about the social lives of the over-70s, was developed by the Soho Theatre and produced at the Pleasance and he later devised, composed and performed Mess with Caroline Horton, which won The Stage Award for Best Ensemble, 2012 and toured internationally.
 
Seiriol’s first musical How To Win Against History, about Henry Cyril Paget, the cross-dressing black sheep Marquis of Anglesey, opened at the 2016 Edinburgh Fringe to critical acclaim, and played two consecutive total sellout runs there in 2016 and 2017. It then toured the UK before transferring to a sellout run at London's Young Vic in December 2017. It has won several awards including a The Stage Award and the Wales Theatre Award.