Ellwood grew up Minnesota. His father, Paul M. Ellwood, Jr., is widely viewed as the "father of the health maintenance organization." He attended the prestigious college prep school, The Blake School, and graduated summa cum laude from Harvard College in 1975 and earned a Ph.D. in economics from the Harvard department of economics in 1981.
He joined the Kennedy School faculty in 1980 and served two separate terms as the School's Academic Dean. He has served as Dean of Harvard University's John F. Kennedy School of Government since July 1, 2004. He is also the Scott M. Black Professor of Political Economy. He is the author of the critically acclaimed, "Poor Support: Poverty in the American Family" (Basic Books, 1988).
In 1993, he was named Assistant Secretary for Planning and Evaluation at the US Department of Health and Human Services (HHS) where he served as co-chair of Bill Clinton's Working Group on Welfare Reform, Family Support and Independence. At HHS, Ellwood played a key role in the administration's development and implementation of critical social policy.
Ellwood is a Fellow of the American Academy of Arts and Sciences, a Research Associate at the National Bureau of Economic Research, and a Senior Research Affiliate of the National Poverty Center at University of Michigan's Gerald R. Ford School of Public Policy. He is also a Faculty Affiliate of the Joint Center for Poverty Research at Northwestern University/University of Chicago and serves on the Board of Abt Associates and the Malcolm Hewitt Wiener Foundation.
In 2016, Ellwood became chair of the US Partnership on Mobility from Poverty, an effort funded by the Bill and Melinda Gates Foundation and run by the Urban Institute. The group of 24 scholars and activists is "a new collaborative aimed at discovering permanent ladders of mobility for the poor. The partnership will identify breakthrough solutions that can be put into action by philanthropy, practitioners, and the public and private sectors."