Antonio has spent most of his political career in Brussels since 1997, where he worked as an assistant to the leader of the Spanish Partido Popular at the European Parliament. He held this position until 1998, when he was called by then-President of the Spanish Government José María Aznar to become his personal advisor for almost four years. In 2002, he returned to Brussels after being elected Secretary General of the European People’s Party, a position he held until 2022. Two years later, he was elected Member of Parliament, holding this position to date. In 2002, under the leadership of the then President of the Government of Spain, José María Aznar, he was elected Executive Secretary of the Centrist Democratic International (IDC-CDI) and continues to hold this position today. Since January 2008, Antonio has been Secretary Treasurer of the Wilfried Martens Centre for European Studies. 

In the previous legislature, from 2019 to 2024, he was the Chairman of the Delegation for Relations with Israel. Currently, he is the Chair of the Delegation to the EU-Mexico Joint Parliamentary Committee (D-MX). He is a Member of the Committee on Foreign Affairs (AFET) and the Subcommittee on Human Rights (DROI). Antonio is also a Member of the Delegation for relations with Israel (D-IL) and the Delegation for relations with the Arab Peninsula (DARP). Furthermore, he is a substitute for the Delegation for Relations with the United States (D-US) and the Committee on Economic and Monetary Affairs (ECON). In addition, he serves as Vice-Chair of the European Parliament Intergroup on Children’s Rights. In 2022, he was named Honorary Vice-Chair of the Conservative European Forum.