In 1986, Ryan appeared in the title role in the musical Elmer Gantry at London's Gate Theatre and followed that with a national tour of the hit show Guys and Dolls, playing the part of Sky Masterson. He returned to the West End to play Neville Landless in the Tony Award-winning musical The Mystery of Edwin Drood and the same year recorded a duet with singer Tom Jones on his album Matador. He also appeared in the video to the Gary Moore single Over the Hills and Far Away from the Wild Frontier album.

In 1993, Ryan toured Europe and Britain playing Figaro in The Marriage of Figaro and Leporello in Don Giovanni, both for Music Theatre, London directed by Nick Broadhurst, followed by a series of open-air concert performances with the Royal Philharmonic Orchestra.

In 1994, Ryan was picked by swordmaster Bob Anderson to assist as sword coach to Richard Gere and Ben Cross in the film First Knight. Director Jerry Zucker also asked him to play John Challenger during the filming.

Before moving to Los Angeles in 1997 Ryan guest starred in many British TV shows including The Bill, Harry, Dempsey and Makepeace, Casualty and Peak Practice. He also appeared in films such as Doomsday Gun and Nil By Mouth. While establishing himself in the US he guest-starred in such TV shows as Frasier, General Hospital, Conan the Adventurer, Passions, Nuremberg and The Young and the Restless. He also worked as Fight Coordinator and Swordmaster on The Secret Adventures of Jules Verne and played Gordon in San Diego's Globe Theatre production of Neville's Island.

In 2000, Ryan played U.S. theatres with original Monty Python member Eric Idle, performing comedy roles in Eric Idle Exploits Monty Python at venues including New York's Carnegie Hall and the Hollywood Bowl. The team later recorded the show exclusively for the Comedy Channel. He then went on to play John Dickinson in the Los Angeles stage production of 1776 directed by Gordon Hunt. Ryan began working on the 2007 film Transformers during filming as the on-set voice of several different robots. This work continued throughout filming and into editing, before the actual casting of voice-over talent. He was then cast as the voice of the character Bumblebee. Ryan also voices Ironhide and Hoist for the Activision video game based on the film. When Ryan was in the studio recording his lines for the actors on set, Michael Bay used the lines Ryan recorded for Bumblebee in the film. But Ryan didn't know that it would be used, and if so he said he would have used a different younger voice. He returned to voice Bumblebee as well as Jetfire for the sequel Transformers: Revenge of the Fallen and the Activision Game based on the film. In early 2009, Ryan continued voice work on Transformers: Revenge of the Fallen working directly with Michael Bay and Alex Kurtzman almost right up to the release of the film.

In 2003, Ryan worked as a swordmaster and fight Director on the film King Arthur directed by Antoine Fuqua. His duties included consulting with the Director and Writer regarding designing all aspects of the knights fighting styles, training all the principal actors including Keira Knightley, Clive Owen and Stellan Skarsgård, planning and choreographing their action.

Ryan played the character of Nasir for the British TV series Robin of Sherwood on which he worked for three years. Nasir was the first Muslim member of the Merry Men - a concept that carried over to later productions such as Robin Hood: Prince of Thieves and the 2006 Robin Hood TV series.

In November 2008, the online publisher ComicMix began running Ryan's The Pilgrim, a graphic novel inspired by factual events during the Second World War and concerning modern psychic warfare research and drawn by comic Artist Mike Grell. It is believed that elements of the story are based on Ryan's experiences during his Service in the Intelligence Corps and Special Forces community. In early 2009 ComicMix announced an agreement with IDW Publishing for hardcopy publishing rights of its online projects and IDW announced the publication of The Pilgrim commencing in April 2010.

During London Book Fair in April 2009, specialist publisher Eddison-Sadd presented the Wildwood Tarot, based on the collector status: Greenwood Tarot authored by Ryan. The Wildwood Tarot is an updated and reworked version of Ryan's original tarot concept, co-written with John Matthews with artwork by Illustrator, Will Worthington. Wildwood Tarot was launched at the Atlantis Bookstore in London in April 2011. Wildwood Tarot remained as the bestselling Tarot and Hottest Bestseller on Amazon.com during the spring of 2011 and has now been translated into German, Dutch, Italian and French. The Wildwood Tarot is published in the US by Sterling Publishing. In 2017, a workbook for The Wildwood Tarot will be released, under the name Wild Magic: The Wildwood Tarot Workbook.

In May 2010 Ryan returned to work on Transformers: Dark of the Moon, once again as the onset voice of the Autobots. Work on this third Michael Bay Blockbuster continued at locations across the US and also at Kennedy Space Center - Cape Canaveral, Florida. The film was shot in 3D with post production voice-work carrying on into the spring of 2011. Ryan contributed several military lines to the final cut of Transformers: Dark of the Moon and was credited as "Military Drone Operator" on the DVD. Ryan also completed Bumblebee lines for the Universal Studios theme park ride based on the films in the autumn of 2011.

In late 2012 he recorded a cameo appearance in the NBC comedy show Community playing Constable Edmund, a new companion to Inspector Spacetime in an homage to BBC TV show Doctor Who. The show aired in early 2013.

In July 2013 Ryan again joined the Transformers franchise, voicing Lockdown in the fourth installment, Transformers: Age of Extinction. In 2014 the film broke worldwide records earning over $1.08 billion in box office receipts. Ryan was nominated in 2015 for the award for best vocal performance in a supporting role in a feature film by Behind The Voice Actors. The character of Lockdown has resonated widely within the Transformers community:

In January 2014 Ryan began playing Mr. Gates in the Michael Bay/Starz production of the pirate show Black Sails and appeared in the first eight episodes of the show which broke all previous viewer records for Starz. The role earned Ryan critical praise for his portrayal of the loyal and even-handed pirate quartermaster:

In 2015 Ryan was nominated for the award for best vocal performance in a supporting role in a feature film by Behind The Voice Actors for voicing Lockdown in Transformers: Age of Extinction. The award eventually went to Stanley Tucci for his work in Mr. Peabody & Sherman.