Chris has also written and illustrated a large number of very successful children's books such as The Wish Factory in 1990, which The Independent described as "magical and inventive - like Heath Robinson with a few drinks inside him." In 1996 he was voted Caricaturist of the Year by the Cartoon Art Trust. Riddell lives in Brighton with his wife, the illustrator and print-maker Joanna Burroughes, and their three children. 

He was taught by renowned illustrator, Raymond Briggs and Riddell acknowledges Briggs as a "huge influence" on his work. Briggs introduced him to his own publisher, and, while still a student, he was commissioned to illustrate The Book of Giants for Sainsburys, which appeared in 1985.

Chris illustrated Pirate Diary by Richard Platt, and Jonathan Swifts Gulliver, both of which won the Kate Greenaway Medal. Something Else by Kathryn Cave won the UNESCO Award amd The Swans Stories by Brian Alderson was shortlisted for the 1997 Kurt Maschler Award and won the 2001 Kate Greenaway Medal.

In 1988 the Europe editor of the Economist, impressed by his book illustrations, hired Riddell to illustrate articles at the magazine, where he remained until 1997.

In 1989 Riddell got his first job as political cartoonist, for the short-lived Sunday Correspondent, and from 1990 to 1991 he was also business cartoonist on the Observer, producing illustrations for the personal finance pages.

In 1991 Riddell moved to the Independent, and also joined the "Business on Sunday" section of the Independent on Sunday. In 1992, with Chris Priestley, a colleague from the Economist, he produced a strip called "Bestiary" for the Independent on Sunday.

In 1995 Riddell became Political Cartoonist on the Observer, for which he also produced the "Antrobus" strip. He won the Macallan Award for the best Labour election cartoon of 1997.

On Fridays Riddell travels from his Brighton home to the Observer office, to produce the cartoon for Sunday’s paper. As he explained to an interviewer in 2008, he listens to the Today programme and skims the Guardian, before catching the train. Here he sits doodling around a blank frame, "but all the time I'm thinking about topics. And always - without fail - an idea forms between Haywards Heath and East Croydon. From East Croydon to London Bridge I write the caption, cross it out, write it again, and so on." At the office he shows his sketch to the editor, then starts work at his desk - one of the few in the office that doesn't have a computer. Here he copies out the sketch, works over it in ink using a soft brush, adding colour wash and goache highlights after drying with a hairdryer.

Riddell has drawn covers for Punch, Economist, New Statesman and Literary Review. He has also written and illustrated a large number of very successful children's books such as The Wish Factory in 1990, which The Independent described as "magical and inventive - like Heath Robinson with a few drinks inside him." In 1996 he was voted Caricaturist of the Year by the Cartoon Art Trust. Riddell lives in Brighton with his wife, the illustrator and print-maker Joanna Burroughes, and their three children. 

In 2010 Riddell explained his method of working in a video for The Guardian. "I like to draw quite politely," he explained,"but I like to be quite rude": "the way that you draw can display anger and savagery, but...I think one can be more devastating by being gentler and kinder. It’s one of those ‘more in sympathy than anger’ approaches, which can be something that politicians find hardest to combat. You know, they can take hate and they can take vitriol, but they can’t take pity quite as well." 

In 2011, as a member of the University of Brighton’s Alumni Network Riddell created the character of Professor C Gull used in booklet and comic form to help engage local primary school children in the idea of participating in higher education.