1 March 1967|
Steffan is a Swansea City supporter.
- The Hollow Crown- Henry vi pt 2 ( 2014)
- Harry Potter and the Deathly Hallows Part I (2010) as Reg Cattermole/Ron Weasley (Polyjuice Potion)
- Under Milk Wood (2014)
- Submarine (2011)
- Ironclad (2011)
- The Big I Am (2010)
- Ali G Indahouse (2002)
- Solomon and Gaenor (1999)
- Twin Town (1997)
- Under Milk Wood- BBC (2014)
- Cucumber (2014)
- Cara Fi (2014)
- A Touch of Cloth III (2014)
- Hinterland (2013)
- Father Brown (2012)
- 4Music (Narrator) (2011–present)
- Teulu (2010)
- Pen Talar (2010)
- Doctors (2010)
- Gavin & Stacey (2007–10)
- Giles Wemmbley Hogg Goes Off.... to Glastonbury (2007)
- Heartbeat (2007)
- Wire in the Blood (2005)
- Con Passionate (2005)
- Belonging (2007-08)
- Tales from Pleasure Beach (2001)
- Bloodline (1997)
- A Mind to Kill (1997)
- Abigail's Party – play by Mike Leigh (Hampstead Theatre, London, England, UK); 2002-03
- The Birthday Party- Clwyd Theatr Cymru; 2006
- The Father- Chichester; 2006
- Great Expectations - Clwyd Theatr Cymru; 2009
- Mary Stuart- Clwyd Theatr Cymru; 2009
- Clybourne Park – Russ/Dan; by Bruce Norris; Royal Court Theatre, London; 2010
- The kitchen Sink- by Tom Wells; Bush Theatre; 2011
- Absent Friends- by Alan Ayckborn; West End; 2012
- Posh- by Laura Wade; West End; 2012
- It's a Mad World My Masters ; Middleton; Royal Shakespeare Company; 2013
- Candide- by Mark Ravenhill; Royal Shakespeare Company; 2013
- I'd Rather Goya Robbed Me Of My Sleep Than Some Other Arsehole- by Federico Garcia; Gate Theatre; 2014
- The Mentalists (play) by Richard Bean; West End; 2015
- The Hairy Ape by Eugene O'Neill; The Old Vic; 2015
- Ni no Kuni: Wrath of the White Witch (2013) – Drippy (voice)
He has also guest-starred in a number of Doctor Who spin-off audio plays produced by Big Finish Productions. These include Dreamtime, The Bone of Contention and as the British Prime Minister in UNIT: The Longest Night and UNIT: The Wasting.
- "Steffan Rhodri". IMDb website. IMDb. 2010. Retrieved 4 May 2010.
- Steffan supports Swans DVD, . . . 'Golden Year' for Gavin, Stacey & Harry Potter star.
- The Actor who will play as Reg Cattermole in the upcoming "Deathly Hallows" movie.
- Reg Cattermole in movies.
- "The Hairy Ape". London Box Office. 2015. Retrieved 17 November 2015.