Stewart was born in 1945 in Folkestone, England. While in the sixth form at Harvey Grammar School in Folkestone he came to the attention of the mathematics teacher. The teacher had Stewart sit mock A-level examinations without any preparation along with the upper-sixth students; Stewart was placed first in the examination. He was awarded a scholarship to study at the University of Cambridge as an undergraduate student of Churchill College, Cambridge, where he studied the Mathematical Tripos and obtained a first-class Bachelor of Arts degree in mathematics in 1966. Stewart then went to the University of Warwick where his PhD on Lie algebras was supervised by Brian Hartley and completed in 1969.^[5]

After his PhD, Stewart was offered an academic position at Warwick. He is well known for his popular expositions of mathematics and his contributions to catastrophe theory.^[6]

While at Warwick, Stewart edited the mathematical magazine Manifold.^[7] He also wrote a column called "Mathematical Recreations" for Scientific American magazine from 1991 to 2001. This followed the work of past columnists like Martin Gardner, Douglas Hofstadter, and A. K. Dewdney. Altogether, he wrote 96 columns for Scientific American, which were later reprinted in the books "Math Hysteria", "How to Cut a Cake: And Other Mathematical Conundrums" and "Cows in the Maze".

Stewart has held visiting academic positions in Germany (1974), New Zealand (1976), and the US (University of Connecticut 1977–78, University of Houston 1983–84).

Stewart has published more than 140 scientific papers, including a series of influential papers co-authored with Jim Collins on coupled oscillators and the symmetry of animal gaits.^{[4][8][9][10][11][12][13]}

Stewart has collaborated with Jack Cohen and Terry Pratchett on four popular science books based on Pratchett's Discworld. In 1999 Terry Pratchett made both Jack Cohen and Professor Ian Stewart "Honorary Wizards of the Unseen University" at the same ceremony at which the University of Warwick gave Terry Pratchett an honorary degree.

In March 2014 Ian Stewart's iPad app, Incredible Numbers by Professor Ian Stewart, launched in the App Store. The app was produced in partnership with Profile Books and Touch Press.^[14]

• Do Dice Play God? The Mathematics of Uncertainty (2019), Profile Books.
• What's the use ?: How mathematics shapes everyday life? (2021), Basic Books.
• What's the use ?: The Unreasonable Effectiveness of Mathematics (2021), Profile Books.

• Easy Programming for the ZX Spectrum (1982), with Robin Jones, Shiva Publishing Ltd., ISBN 978-0-906812-23-5
• Computer Puzzles For Spectrum & ZX81 (1982), with Robin Jones, Shiva Publishing Ltd., ISBN 978-0-906812-27-3
• Timex Sinclair 1000: Programs, Games, and Graphics, with Robin Jones, Birkhäuser, ISBN 978-3-7643-3080-4
• Spectrum Machine Code (1983), with Robin Jones, Shiva Publishing Ltd., ISBN 978-0-906812-35-8
• Further Programming for the ZX Spectrum (1983), with Robin Jones, Shiva Publishing Ltd., ISBN 978-0-906812-24-2
• Gateway to Computing with the ZX Spectrum (1984), Shiva Publishing Ltd., ISBN 978-1-85014-053-5

• The Science of Discworld, with Jack Cohen and Terry Pratchett
• The Science of Discworld II: The Globe, with Jack Cohen and Terry Pratchett
• The Science of Discworld III: Darwin's Watch, with Jack Cohen and Terry Pratchett
• The Science of Discworld IV: Judgement Day, with Jack Cohen and Terry Pratchett

• Catastrophe Theory and its Applications, with Tim Poston, Pitman, 1978. ISBN 0-273-01029-8.
• The Foundations of Mathematics, 2nd Edition, Ian Stewart, David Tall. Oxford University Press, 2015. ISBN 978-0-19-870643-4
• Algebraic number theory and Fermat's last theorem, 4th Edition, Ian Stewart, David Tall. Chapman & Hall/CRC, 2015 ISBN 978-1-49-873839-2
• Complex Analysis, 2nd Edition, Ian Stewart, David Tall. Cambridge University Press, 2018. ISBN 978-1-10-843679-3
• Galois Theory, 5th Edition, Chapman & Hall/CRC, 2022 ISBN 978-10-3210159-0 Galois Theory Errata for 3rd Edition

• Wheelers, with Jack Cohen (fiction)
• Heaven, with Jack Cohen, ISBN 0-446-52983-4, Aspect, May 2004 (fiction)

In 1995 Stewart received the Michael Faraday Medal and in 1997 he gave the Royal Institution Christmas Lecture on The Magical Maze. He was elected as a Fellow of the Royal Society in 2001.^[2] Stewart was the first recipient in 2008 of the Christopher Zeeman Medal, awarded jointly by the London Mathematical Society (LMS) and the Institute of Mathematics and its Applications (IMA) for his work on promoting mathematics.^[17]

Stewart married Avril, in 1970.^[2] They met at a party at a house that Avril was renting while she trained as a nurse. They have two sons.^[2] He lists his recreations as science fiction, painting, guitar, keeping fish, geology, Egyptology and snorkelling.^[2]

• Ian Stewart at the Mathematics Genealogy Project
• Personal webpage