With all precincts reporting, Bill White had 136,617 votes to 81,824 for Orlando Sanchez, or 63 percent to 37 percent.
White, 49, a former chairman of the Texas Democratic Party, spent some $2.2 million of his own fortune as part of a record $8.6 million effort in the race against Cuban-born Sanchez, a Republican making a second bid to become Houston's first Hispanic mayor.
The race was officially nonpartisan but White's election would give Democrats a rare victory in President Bush's home state, where Republicans hold every major statewide elected office.
White topped eight other candidates in last month's election with 38 percent of the vote, falling short of the 50 percent he needed to win outright and succeed Lee Brown, barred by term limits from seeking a fourth two-year term. Sanchez, who narrowly lost to Brown two years ago, was second with 33 percent.
A Houston Chronicle-KHOU-TV poll published Friday showed White with a commanding 53 percent to 35 percent lead, with 12 percent of voters undecided and an error rate of 4 percentage points. A total of 625 registered voters were surveyed last week.
White, who had Brown's support, touted bipartisan support and stayed with a yearlong campaign theme to "get Houston moving."
Sanchez, 46, endorsed by the state's top Republicans, portrayed himself as a reformer and said White's election would be a continuation of current tax and spending policies that have put the city $20 million in debt.