Sean is a graduate in chemistry of the Universities of London (King's: BSc 1960) and Chicago (PhD 1973). From 1960 to 1963 he taught science and mathematics at Bishop Herman College, Kpando, Ghana; he was also a part-time adult education teacher for the Institute of Public Education of the University of Ghana. He came to the United States as a graduate student and lived for a year at the Chicago International House. Later, he was a Senior Research Chemist in the Central Research Department of the Monsanto Company in St Louis. Back in London in the 1970s, he taught for a year at Wimbledon College; served as a branch secretary in the Ealing North Constituency Labour Party, which he represented on the Brent Community Health Council and the Ealing Community Relations Council; and was a delegate to the National Association of Community Relations Councils. In Chicago in the 1980s and 90s he volunteered at the Crossroads International Student Center (which he served as Board Member and Treasurer); Hyde Park Cooperative Homes (Board Member and President); and Jyoti Childen's Development Foundation (of which he was a Board Member for more than ten years). He also chaired the University of Chicago High School Parents' Association.

Seán was born in an English village to more or less Irish parents.  He has spent most of his adult life in Foreign Parts (notably the United States) has lived in three countries and visited another thirty. His wife, Andrea Bjorklund, teaches in the UC Davis law school.  He has two adult daughters, one in Boston and the other in Chicago. Their mother, the late Diana Woo, was a neonatologist who taught at the University of Chicago medical school.  Seán and Andrea have lived in Davis since 2003, and he joined the board in 2006.