Gallegos, who died last month, remained on Tuesday's ballot because he passed less than 74 days before the election and the liberal Hispanic easily won re-election to his Fort Worth-area seat posthumously.
"He was always there for the community," longtime friend and retired firefighter Juan Hernandez told the Houston Chronicle.
Gallegos died of complications from liver disease in October.
"Every person who came up to me was like, 'Didn't he die?'" Cynthia Gallegos, his youngest sister, said in southeast Houston where the family gathered for Election Night. "I would bite my lip and explain the process. We want to keep the district Democratic."
Under Texas law, Republican Gov. Rick Perry will declare the seat vacant and schedule a special election within 45 days.
Gallegos' brother-in-law, Johnny Villarreal, smoked a hand-rolled cigar from the winner's private humidor and said, "He [Gallegos] will be smiling all the way."