Mr. Abad was a trade unionist of the Federation of Free Workers and Ateneo Workers College from 1976 to 1979 and was research director of Ateneo Center for Social Policy and Public Affairs. 

When the Congress of the Philippines was restored in 1987, Mr. Abad launched his successful congressional bid to represent the Lone District of Batanes where he became a staunch advocate of agrarian reform in the national legislature. 

He held the position until his appointment to his brief stint as Secretary of the Department of Agrarian Reform and ran again for Congress in 1995, completing his third and final term in 2004. On July 2004, then-President Gloria Macapagal-Arroyo appointed Abad as Secretary of the Department of Education. 

Aside from his stints at the Department of Agrarian Reform, and the Department of Education, Mr. Abad also held various cabinet-level positions in the past, including serving as Secretary of the Philippine Department of Budget and Management during the term of the (Fmr) Pres. Benigno S. Aquino III. 

Mr. Abad likewise served as party president of the Liberal Party of the Philippines and is a convenor and former chairperson of the Council of Asian Liberals and Democrats.