Gallegos was elected to the State Senate in 1995 and served the Sixth District that included parts of Houston and Harris County. He had also earlier served two terms as a State Representative from Houston and had spent more than two decades as a Houston firefighter before he became a politician.
Gallegos had undergone a liver transplant in 2007 and died from complications at the Methodist Hospital.
Friend and colleague Senator John Whitmire says Gallegos was proud to be the first Hispanic State Senator from Houston.
"The Hispanic community needed a voice in the State Senate from Houston, and Mario provided it. He regularly took on our institutions like HISD and the Port and the rodeo to make certain that they gave opportunity for all Houstonians. But he was so proud to be a Hispanic State Senator and that's what he'll be remembered for in my mind, for being a voice in his community."
Gallegos was up for re-election next month and it's too late to remove his name from the ballot. If he wins the election, Governor Rick Perry will have to call a special election to replace him.
Funeral services are planned for later this week here in Houston. Mario Gallegos Jr. was 62 years old.