He has made guest appearances on Highlander: The Series as Kronos, an enemy of Duncan MacLeod (Adrian Paul) and former acolyte of Methos (Peter Wingfield) in the episodes “Comes a Horseman”, “Revelations 6:8”, “Archangel” and “Not To Be”. He starred in the 1986 TV series Crossbow (UK, William Tell) as Roland.

He also guest starred in the 1990 TV series Zorro in the episode “All that Glitters” which preceded his starring role as the military governor, Colonel Montoya, in the 2000 syndicated TV series Queen of Swords. Peter Wingfield also co-starred as Dr Robert Helm. The part of Montoya was written for Pelka by executive producer David Abramowitz who in October 1999 offered him the part subject to approval by the other show producers.

In 1999, he appeared in the British TV soap opera Family Affairs as Simon Thornton. His sister, Kazia, was also a leading player in Family Affairs; however, that was after Valentine had appeared in the soap opera. Of the feature films in which Valentine has performed, the best-known was Roman Polanski’s 2002 film The Pianist. His supporting comedic role in Under the Tuscan Sun was performed mute. He returned to stage work in 2013 when he reprised his role as John Lennon in Sandy Marshall’s biopic And in the End at the Jeremy Street Theatre in London.

Also in 1999, he had a guest starring role in Highlander: The Raven as Andre Korda, an immortal who is a criminal and once trained the main character Amanda. The episodes were ‘The French Connection’ and ‘A Matter of Time’.