The trivia-mad 64-year-old has racked up 30 appearances on game shows including Fifteen to One, Eggheads, The Chase and The Weakest Link and this week he was awarded a place in the Guinness Book of Records.
From Sunday night the father-of-two will star in a new four-part ITV show called Come On Down! The Game Show Story, which will take viewers on a trip down memory lane looking at the history of British television quiz shows.
Mr St John from Cannock said: "A couple of months ago ITV got in touch with me and said they would like me to do a skit with Bradley Walsh for a new documentary about quiz shows.
"I went to Manchester to film the short piece and it will be shown on ITV at some point in the next four weeks.
"Bradley was great fun and I can't wait to see what it looks like on the TV."
Mr St John's love affair with game shows began in 1982 when he appeared on Sale of the Century.
He stormed to victory and won two motorcycles before going on to face Daphne Fowler, now known as a team member on BBC two show Eggheads, in an Australian version of the show.
Over the years he has won cash prizes for coming top of the scoreboard on shows such as Winner Takes All and Chain Letters in 1987, Star Quality in 1990, No Win No Fee in 2002 and Face the Clock in 2013.
But Mr St John says his biggest achievement is securing a place in the Guinness Book of Records.
This week he was crowned Britain's Most Prolific TV Quiz Show Contestant and now holds the record for the Most TV Quiz Appearances.
He said: "In January I wrote to the Guinness Book of Records and I sent them clips and footage to prove that I had been on 30 shows.
"This week they confirmed that my name will be in the book which I find really funny because I am not a professional quizzer or an egghead, I just do it for fun.
"When I first started taking part in quiz shows I never knew it would lead to this. I can't wait to receive my certificate"
Mr St John is currently writing a book about his experiences as a regular game show contestant, which he hopes to release on Kindle books next week.
The book gives readers advice on how to apply to become a contestant and deal with pressure under the spotlight.
There are also chapters about the 30 game shows he has appeared on.
Mr St John added: "I am not an expert by any means I think it all comes down to luck.
"I tried numerous times to get on Who Wants to be a Millionaire but unfortunately I never did and I have auditioned to be a contestant on Mastermind numerous times.
"I haven't been on a show for over a year now and I am starting to get withdrawal symptoms so I will have to apply to go on some more soon."