Alonso José Puerta received a degree in Roads, Canals and Ports Engineering from the Technical University of Madrid. In 1972, José Puerta joined the Spanish Socialist Workers' Party and five years later became Secretary General of the Spanish Socialist Workers' Party of the Community of Madrid. He was appointed deputy to the Constituent Cortes by the electoral district of Madrid and, in 1979, councilor of the City of Madrid, where he held the responsibilities of deputy mayor and spokesman of the Socialist Group until his expulsion of the PSOE in 1981 for opposing the irregular awarding of contracts. In 1982, he joined the Socialist Action Party and 4 years later he was a founding member of the United Left coalition becoming member of the Federal Presidency.
In 1987, Alonso Puerta was elected member of the European Parliament and remained an MEP until 2004. During that period he was member of the Communist and Allies Group, member of the Group for the European United Left, member of the Confederal Group of the European United Left, member of the Confederal Group of the European United Left/Nordic Green Left, Vice-Chair of the Committee on Transports and Tourism, Vice-President of the Parliament's Bureau, Vice-President of the European Parliament, member of the Committee on Institutional Affairs, member of the Committee on the Environment, Public Health and Consumer Protection, member of the Membres fron the European Parliament to the Joint Assembly of the Agreement between the African, Caribben and Pacific States and the EEC (ACP-EEC), member of the Committee on the Environment, Public Health and Consumer Protection, member of the Delegation for relations with the countries of South America, member of the Committee on Foreign Affairs and Security, member of the Subcommittee on Security and Disarmament, member of the Delegation for relations with the countries of South America, member of the Delegation for relations with Russia, member of the Delegation for relations with the countries of South America and MERCOSUR, member of the Committee on Regional Policy, Transport and Tourism, member of the Delegation for relations with Australia and New Zealand and member of the Delegation for relations with the countries of Central America and Mexico.