|Born||1 March 1967|
|Gavin & Stacey (2007–2010, 2019)|
Steffan is a Swansea City supporter.
- Twin Town (1997) - Hunky
- Solomon and Gaenor (1999) - Noah Jones
- Ali G Indahouse (2002) - School Teacher
- Cymru Fach (2008)
- The Big I Am (2010) - DS Moseley
- Submarine (2010) - Mr. Davey
- Harry Potter and the Deathly Hallows: Part 1 (2010) - Reg Cattermole
- Ironclad (2011) - Cooper
- Under Milk Wood (2015) - Mog Edwards
- Wonder Woman (2017) - Colonel Darnell
- Last Summer (2018) - Sgt Morgan
- A Mind to Kill (1997) - Young Sir Isaac Gwillym
- Tales from Pleasure Beach (2001) - Wes
- Con Passionate (2005) - Andy
- Wire in the Blood (2005) - Bill Denton
- Heartbeat (2007) - Frank Jepson
- Belonging (2008) - Ed
- Giles Wemmbley Hogg Goes Off.... to Glastonbury (2007, TV Movie)
- Gavin & Stacey (2007–2010) - Dave
- Doctors (2010) - Gerry Cutler
- Pen Talar (2010) - Phillip Harrison
- Teulu (2010)
- 4Music (2011–present) - Narrator
- Father Brown (2012) - Christy Nolan
- Hinterland (2013) - Herbert Rees
- Under Milk Wood (2014, BBC) - Mr. Waldo
- A Touch of Cloth (2014) - Eddie Huffway
- Cara Fi (2014) - Vic Reed
- Cucumber (2015) - Don Baxter
- The Hollow Crown (2016, BBC) - Oxford
- Apple Tree Yard (2017, BBC) - DI Cleveland
- Shorts: The Pines (2017, by Gary Owen) (starring Steffan Rhodri)
- Three Girls (2017, BBC) - Fraser Lavery
- Keeping Faith (2017-2019, BBC) - Judge Gwyn Daniels
- A Very English Scandal (2018, BBC) - D.C.S Michael Challes
- Manhunt (2019, ITV) - DC Neil Jones
- Temple (2019, SKY) - Jeremy
- 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 by Richard Bean; West End; 2015
- The Hairy Ape by Eugene O'Neill; The Old Vic; 2015
- Walter Harrison in This House by James Graham; Garrick Theatre; 2016-17
- Killer Joe by Tracy Letts at Trafalgar Studios; 2018
- 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 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.
- Price, Karen (20 November 2009). "Steffan Rhodri: I'm a Jack of all trades".
- "The Hairy Ape". London Box Office. 2015. Retrieved 17 November 2015.
- "February 2017-publisher=London Garrick Theatre-year=2016".
- "Re-imagining Ni no Kuni for the West".