He was born in Buenos Aires but moved to the United States in 1946 during the Perón regime with his father Amado Alonso, a leading Spanish philologist, who was then appointed at Harvard. He earned a bachelor's degree in architectural science from Harvard in 1954 and a master's degree in city planning from Harvard University's Graduate School of Public Administration in 1956. In 1960 he received a doctorate in regional science from the University of Pennsylvania.
In 1976 Alonso became Director of the Center for Population Studies of Harvard University. Two years later he became the Richard Saltonstall professor of population policy in the Faculty of Public Health and a member of the Department of Sociology in the Faculty of Arts and Sciences.
His research was focused on demographic changes, in particular in very urbanized areas. He developed a mathematical model connecting migration and the evolution of the distribution of population.
In 1964, he published Location and Land Use, in which he defined a modeled approach to the formation of land rent in urban environments. His model became one of the pillars of urban economics.[2]