Mitchinson acted as an associate producer for the first series. For several years Mitchinson was also director of the QI Club, which was situated at 16 Turl Street, Oxford. Under his management the building consisted of a bookshop, a café-bar and a vodka bar, as well as a number of rooms devoted to use by the private members club.

After the success of the [QI] TV series, Mitchinson went on co-author with QI's creator John Lloyd the QI Annuals for 2008 and 2009,; as well the main QI books: These being The Book of General Ignorance, The Book of Animal Ignorance,, Advanced Banter, a book of quotations,, and The QI Book of the Dead.

As of November 2008, Amazon.co.uk reported that the Book of General Ignorance was fourth in its five best selling titles in the ten years it has been in operation, behind the two last Harry Potter novels and The Dangerous Book for Boys.

For the ten years before QI, Mitchinson was a book publisher, running the Harvill Press, Cassell & Co and acting as Deputy Publisher of the Orion Group, now the UK’s third largest publisher. Prior to that he spent six years as Marketing Director of Waterstone’s the booksellers.

John is a Vice-President of the Hay Festival, a director of Jonathan Burrows contemporary dance group, a Fellow of the RSA and one of Trustees of the London Centre for International Storytelling.

John lives in the Oxfordshire village of Great Tew where spare time is consumed by rare breed pigs, chickens, vegetables and small children, though not necessarily in that order.