His backstage participation in the Taif conference in Saudi Arabia, which ended the destructive Lebanese civil war, made him ambassador to the United States of America. In 1991, he was appointed Maronite parliamentarian of the Metn region. He was later re-elected in organised legislative elections in 1992, 1996 and in 2000.
From the beginning of his political life, he situated himself in the opposition to the pro-Syrian governments that ruled the country. He opposed the economic policies of the late prime-minister Rafiq Hariri and to Syrian interference in the Lebanese political scene. He voted against the constitutional amendments imposed by Syria to extend the mandates of presidents Elias Hrawi (in 1995) and Emile Lahoud (in 2004).
The same year, he founded along with about two hundreds and fifty Lebanese intellectuals (of which Misbah Ahdab, Camille Ziadé, Nadim Salem, Antoine Haddad, Ziad Baroud, Wafic Zantout, Mona Fayad, Hareth Sleiman,Malek Mroueh, Melhem Chaoul...) The Democratic Renewal Movement. A movement that presents itself as a reformist and laic, opposition political movement. Despite being defamed by traditionalists, and populists, Lahoud and the DRM are extremely respected among intellectual circles.
He was a prominent figure of the anti-Syrian opposition movement that started to organise itself after the extension of the pro-Syrian president Emile Lahoud's term and which gained more political weight following the assassination of Rafiq Hariri on 14 February 2005.
The Democratic Renewal Movement is part of the March 14 Alliance, an anti-Syrian coalition (also regrouping Saad Hariri's Future Movement, Amine Gemayel's Kataeb Party, Elias Atallah's Democratic Left, Carlos Éddé's National Bloc and Dory Chamoun's National Liberal Party). Nassib Lahoud took part in the 2005 legislative elections in his Metn district , at the head of the opposition list. He lost the elections against Michel Aoun's Free Patriotic Movement and allied pro-Syrian figures.
Nassib Lahoud is since 1995 considered to be the most serious candidate for the presidency. Despite his defeat in the last parliamentary elections, he announced that he was prepared to run for president if the March 14 Alliance that holds a majority in parliament since the last elections backs him. His willingness to run for the presidency is part of a wider campaign to remove the pro-Syrian president Emile Lahoud (Nassib's cousin) who is widely considered to be the last bastion of Syrian hegemony over the country.