After finding a Roman coin as a teenager, Bendall became a collector, researcher and dealer in ancient coins. After leaving Cheltenham College, he did military service (1956-58), partly in Germany, then studied part-time at the Institute of Archaeology, University of London (1962-1965), while working in the coin department of Spink & Son (1959-1965). He was later elected a Fellow of the Society of Antiquaries. Bendall worked for several specialist coin dealers: the coin department of Spink & Son (1959-1965), A.H. Baldwin (1967-1987), Numismatic Fine Arts in Los Angeles (1987-1988), and in 1998 catalogued the first sale of the Byzantine gold coins from the Nelson Bunker Hunt Collection for Sotheby’s, New York. In the 2000s he rejoined Spinks in London (2006-2010). He was elected as an Honorary Fellow of the Royal Numismatic Society in 2010. His collection of Byzantine coins was stolen in London in February 2018. Bendall died on 26 June 2019.
Bendall wrote several books on Byzantine coins and weights, and over 200 articles on coins, military history and jewellery. They include:
- (with P.J. Donald) The Later Palaeologan Coinage: 1282-1453 (London: Baldwin, 1979)
- (with Cécile Morrisson) ‘Un trésor de ducats d’imitation au nom d’Andréa Dandolo (1343-1354)’ (Revue Numismatique 6e sér. 21, 1979)
- ‘Palaeologan gold coins from the mint of Thessalonica (Schweizer Münzblätter 125, 1982)
- (with David Sear and Michael Dennis O'Hara) Byzantine Coins and their Values (London: Seaby, 1987)
- A Private Collection of Palaeologan Coins (Wolverhampton, 1988)
- ‘The coinage of Constantine XI’ (Revue Numismatique 6e sér. 33, 1991)
- Byzantine Weights: An Introduction (London: Lennox Gallery, 1996)
- ‘The Byzantine coinage of the mint of Jerusalem’ (Revue Numismatique 159, 2003)
- An Introduction to the Coinage of the Empire of Trebizond (London: Spink, 2015) – the first major work on this subject.
- "Bendall, Simon". Coinsweekly.com. Retrieved 24 July 2019.
- "Simon Bendall (1937-2019)". Coinsweekly.com. Retrieved 26 July 2019.
- "Honorary Fellowship". The Royal Numismatic Society. May 23, 2014.
- "Byzantine scholar's entire collection stolen after break-in". Antiquestradegazette.com.
- "In memory of Simon Bendall". Retrieved 17 November 2019.