Sean joined Peat, Marwick Mitchell & Co (now KPMG) in 1972 beginning a career which would encompass audit, taxation, financial investigations and consulting.
He became a partner on his transfer to the Malaysian practice in 1985, where he led the financial services practice as well as the technical advisory department. On his return to London, he assumed responsibility for the firm's leasing practice and then the telecommunications and media practice, for which he was global leader for more than 10 years. After a second period in Asia, directing the Asia-Pacific practice from 2009 to 2012 from Singapore, he retired from KPMG. For over three years he was the Senior Independent Director and Audit Committee Chairman of Millennium & Copthorne Hotels plc. He is currently the Audit Committee Chairman for Jersey Telecom, Crown Representative at the Cabinet Office, a Member of Council of the Royal Society for Asian Affairs and Deputy Chairman for Arthritis Research UK.