He is an alumnus of the Scuola Normale Superiore di Pisa. He first came up to Cambridge in 1985, before becoming a Junior Research Fellow at Churchill College in 1987. After spending two years at the Department of History at Newcastle, he became an Assistant Professor of Modern British History at Princeton. In 1996 he came back to Cambridge as a College Lecturer at Robinson College. He then became a University Lecturer in 1998 and a Reader in 2000. In 2008 he moved back to his old College, Sidney Sussex. In 2011 he was appointed to a personal chair and he is now Professor of Modern and Contemporary History.

His research focuses on the social, economic and political history of democracy. He has written on Gladstonian liberalism and the Italian Risorgimento, but Ireland is his main area of research. His British Democracy and Irish Nationalism, 1876-1906 (Cambridge University Press, 2007) examined the way the Irish Home Rule campaigns affected the making of democracy in the two islands. He has published (with Daniel Mulhall), The Shaping of Modern Ireland (Irish Academic Press, 2016) and edited (with Mary Daly), The Cambridge Social History of Ireland since 1740 (Cambridge University press, 2016). His current research focuses on the history of religious and ethnic minorities in twentieth-century Ireland, in a comparative perspective. He focuses on the challenge of nation building, the redefinition of ‘public interest’, civil liberties and ‘the constitution’ in deeply divided societies.