Congressman Al Green played a pivotal role in getting Locke and Hall to talk through their potential candidacies.
Both men are former city attorneys, and experts have said they could split the crucial African-American vote if both remained on the ballot.
On Monday, all three appeared together, saying Locke will be their candidate.
"It is in the best interest in the city that we both not compete for the same constituency," said Hall Monday morning. "And so with that, I gladly and freely withdraw my name and support Gene Locke."
"I have benefitted from the ideas he's expressed about how we should govern Houston," said Locke. "I've been energized by his pledge of support."
So for now, it's a three-way race for mayor. Besides Locke, city Controller Annise Parker and city council member Peter Brown have announced their candidacies.