On August 21, 1971, the bombing at Plaza Miranda marred a Liberal Party rally, killing 9 persons and injuring 92 more, including Lopez, who was then a city councilor.

When Marcos declared martial law, Lopez decided to organize active opposition to the regime that could eventually topple it and help restore democracy to the country.

Lopez was among the founding signatories of Laban, a contraction of “Lakas ng Bayan” and a Tagalog translation of People's Power.

Marcos' ticket, the Kilusang Bagong Lipunan (KBL), suffered a heavy blow and the UNIDO candidates including Lopez and four others won.

While serving in the Batasang Pambansa, he filed bills aimed at proposing the compensation income of spouses who are both employees to be taxed separately, paying lower taxes, seeking to abolish the Metro Manila Commission, providing for the establishment of the Philippine National Language Commission, and providing for a synchronization of national and local elections in 1986.

[4] During the 1988 elections, he ran for a full term under the PDP-LABAN and won, defeating Lito Atienza and Eva Estrada-Kalaw, both his fellow former delegates at the Batasang Pambansa.

In January 1990, Lopez padlocked two Manila casinos operated by the Philippine Amusement and Gaming Corporation (PAGCOR), saying the billions it gained cannot make up for the negative effects gambling inflicts upon the people, particularly the youth.

[7] He last served as chairman of the Philippine National Oil Company and Pacific Concrete Products Inc.[8] Lopez died on New Year's Day, January 1, 2017, at St. Luke's Medical Center in Quezon City due to a heart attack at the age of 81.

11280 to officially rename a portion of Radial Road 10 to Mel Lopez Boulevard, which runs from Anda Circle in Manila up north to Estero de Marala at the city's border with Navotas.