After receiving his B.A. in Economics from Bocconi University of Milan and his PhD in Sociology from the University of California, Berkeley, Martinelli started teaching at the University of Milan(Università degli studi di Milano),where he became full professor of Economic sociology in 1980 and of Political Science in 1987. Between 1987 and 1999 he was Dean of the Faculty of Political and Social Sciences of the University of Milan. He is now President of the Degree course in Political Sciences and of the Post-graduate course in Politics and Government. He also taught Sociology at Bocconi University of Milan and Political Science and Sociology in various foreign universities, among which the University of California, Berkeley, Stanford University, New York University, University of Valencia, Ain Shams University in Cairo and the Saint Petersburg State University. In 1998-2002 he was elected President of the International Sociological Association. He is member of the Executive Committee of the International Social Science Council. He is a member of the Real Academia des Ciencias Morales y Politicas de Espana.

Martinelli has coordinated and participated in major international research projects, like ‘Business Interests Associations’, ‘Comparative Charting of Social Change’, ‘Sustainability for the 21.st Century: Overcoming Limits to Creative Adaptation’.

He has been member of Italy's National Council of Science and Technology for its whole duration. He is member of the Scientific Committee of the Regional Institute of Research of Lombardy (IRER).He is member of the Scientific Committees of the Italian Foundation for the diffusion of corporate social responsibility (I-CSR). Between 2001 and 2006 he has been elected in the Milan City Council. He is on the editorial board of several scientific journals and writes for newspapers and magazines, including Il Corriere della Sera.In 40 years of scholarly work he has written books and essays on political and sociological theory, development and modernization studies, international relations and global politics, entrepreneurship and management, corporate social responsibility, complex organizations, interest groups and policy-making.His recent interests focus on corporate social responsibility and sustainable development, the comparative analysis of political and social systems, and the models and actors of global governance.