Steffan trained at Guildhall School of Music and Drama.

Theatre includes: Winter’s TalePericles; Romeo and JulietA Midsummer Night’s DreamTitus Andronicus (Shakespeare’s Globe), Y Tŵr/The Tower (Invertigo Tour); A World Elsewhere (Theatre503); Journeying Boys (Barbican); Outside on the Street (Pleasance Edinburgh, Arcola Theatre); The Winslow Boy (Theatr Clwyd); Saer Doliau/Doll Mender (Finborough Theatre); I am Not Manuel (Teatre Lliure, Barcelona).

Television includes: London Spy (BBC).

Steffan is Joint Artistic Director of Invertigo Theatre Company, and has adapted My People (co-production with Theatr Clwyd), and is currently developing their new one-man show, My Body Welsh.