In 1990, he was elected as municipal legislator for the municipal legislative assembly of San Juan, as president of the New Progressive Party of Puerto Rico for the representative district III of San Juan, and as president of the Republican Party for the same district.
He was sworn on January 11, 1993, effectively becoming an official member of the 24th House of Representatives of Puerto Rico.
He was sworn on January 13, 1997, effectively becoming an official member of the 25th House of Representatives of Puerto Rico.
In 1999, he decided to no longer run for the House of Representatives but publicly supported and campaigned for Carlos Pesquera, then gubernatorial candidate for the New Progressive Party.
Díaz Urbina married Zulma Ivelisse Fuster Troche, a prosecutor for the district of San Juan, in 1997.