Valenzuela was born Arturo Arms Valenzuela Bowie in Concepción, Chile to American Methodist missionaries Raymond Arms Valenzuela and Dorothy Denell Bowie Marsh. He spent his childhood in Concepción where he attended primary school at the "Lycée Charles de Gaulle", where he learned to speak French. In 1960, after his school was destroyed by the Great Chilean earthquake, he was sent by his family for a year to the United States. During the next eight years, he went back to visit his family in Chile only once. He earned a B.A. summa cum laude in Political Science and Religion from Drew University in 1965 and then obtained an M.A. (1967) and Doctorate (1971) in Political Science focusing on Comparative Politics from Columbia University. His doctoral thesis was entitled "Clientelistic Politics in Chile: An Analysis of Center Local Linkages".