[3] An Emeritus Professor of Commerce of Gresham College,[4] and founder of the Long Finance initiative, Mainelli has been Alderman for Broad Street Ward in the City of London since 4 July 2013,[5] and was elected Sheriff on 24 June 2019, serving for two terms.

[8] From 1973 to 1977, Mainelli attended Bishop Moore High School in Orlando, Florida, where he was first introduced to computing, and spent three summers working as a programmer for Martin Marietta on missile guidance systems.

[8][9] Mainelli attended Harvard University where he was a resident of Dunster House[10] and graduated with a BA degree in Government in 1984, including a year reading Engineering and Mathematics at Trinity College Dublin (1980/81).

[7] Mainelli later completed an MPhil (1997) and PhD (2004) at the London School of Economics in chaotic systems[11] with a doctoral thesis titled Development of a risk-reward meta-methodology,[12] under the supervision of Ian Angell.

[34] Mainelli was elected an Honorary Bencher of Middle Temple in February 2023, [35] and was appointed President of the London Chamber of Commerce & Industry on 15 January 2025.

[6] In view of the global disruption to public life brought about by the COVID-19 pandemic, Mainelli was re-elected, on 24 June 2020, to serve a second term as Sheriff of London for 2021.

[56] Mainelli's mayoral theme was 'Connect To Prosper', an initiative that aimed to highlight the City of London's ability to solve global challenges.

[62] Mainelli's economics book, The Price of Fish,[63] also written with Ian Harris, applied his Gresham lecture series ideas to "wicked problems".