After joining Arthur Andersen in 1985, Mainelli became a senior partner and board member of the accountancy firm BDO Binder Hamlyn from 1987 to 1994. At Gresham College, as a Visiting Professor, Mainelli lectured on new concepts of money and the role of government. He delivered and published a series of 28 free one-hour lectures on commerce at Gresham College in the City of London while serving as Mercers School Memorial Professor of Commerce from 2005 to 2009. The theme of his programme was “Society’s Commercial Choice – Risks and Rewards of Markets”. In 2005 Mainelli, Z/Yen in conjunction with Gresham College, the City of London Corporation and forty financial institutions, launched Long Finance's London Accord, an agreement to share environmental, social and governance research with policy makers and the public. While co-founding Z/Yen in 1994, Professor Mainelli had a spell in merchant banking with Deutsche Morgan Grenfell and served as Corporate Development Director of Europe's largest R&D organisation leading to two privatisations. At Z/Yen, Mainelli established the Global Financial Centres Index, The London Accord, , the Global Intellectual Property Index, the Global Green Finance Index, the Farsight Award, and other financial services initiatives. His area of current research encompasses the research programme and he speaks quite frequently on his two decades of research on 'smart ledgers' as well as other technologies. Mainelli is a chartered certified accountant, computer specialist, securities professional and management consultant. He is a non-executive Director of the United Kingdom Accreditation Service where he is a proponent for competitive standards markets, and two AIM-listed companies, PCGE plc, and Wishbone Gold plc. He is a Fellow and Trustee of Gresham College and a former Visiting Professor of the London School of Economics. In 2013, Mainelli was elected Alderman of Broad Street for the City of London Corporation. In 2015 he was awarded the title of Consigliere del Senato Accademico of L’Accademia Tiberina. Master of the Worshipful Company of World Traders for 2017–18, he has held advisory posts at City University, Hitachi UK, and HM Treasury. Mainelli was elected Sheriff of the City of London on 24 June 2019 and assumed office on 27 September 2019.
1996 Foresight Challenge Award for visualising risk in the Financial Laboratory
2003 UK Smart Award for prediction software, and was British Computer Society “Director of the Year”.
Writing
Mainelli has published over 50 journal articles, 200 commercial articles and four books, including the novel, "Clean Business Cuisine: Now and Z/Yen", written with Ian Harris. Mainelli's economics book, "The Price of Fish", also written with Ian Harris, applied his Gresham lecture series ideas to 'wicked problems'. "The Price of Fish" won the 2012 Independent Publishers Gold Award for Finance, Investment and Economics.
Publications
Novels
Michael Mainelli and Ian Harris, , Milet Publishing,, 160 pages.
Non-fiction
Abdeldjellil Bouzidi and Michael Mainelli, ', Revue Banque,, 123 pages.
Michael Mainelli and Ian Harris, ', Nicholas Brealey Publishing,, 328 pages .
Ian Harris and Michael Mainelli, , ICSA Publishing,, 224 pages.
Personal life
Mainelli married in 1996 Elisabeth and together they undertook the restoration of the Thames Sailing Barge "SB" Lady Daphne, while he still lectures on, and supports, sailing barges and their history. He has been an International Member, International Financial Services Industry Advisory Committee, Office of the Taoiseach – Dublin, Ireland since 2015.