Garcia, who lost in a run-off to Emanuel in the 2015 election, announced his decision at a union hall meeting before the Southside Irish Parade on Sunday.
"She will become the change agent that Chicago needs so desperately at this critical juncture," he said.
Garcia’s support has been coveted since the February election left Lightfoot and Cook County Board President Toni Preckwinkle to compete in a run-off race. Both candidates had private meetings with Garcia, but he ended up choosing Lightfoot despite his connections with Preckwinkle.
The board president had made note of Garcia’s role in her political career after she met with him, discussing how she had appointed Garcia her floor leader when both were serving on the Cook County Board. She did not endorse him in his race to unseat Emanuel in 2015, however.
Ever since Garcia lost his race against Emanuel, he has only seen his political power grow. He has become the most prominent Latino leader in Chicago, and won a campaign to replace Congressman Luis Gutierrez last fall.
Former mayoral candidate Jerry Joyce, who finished with roughly 7.2 percent of the vote in the February election, also added his support to Lightfoot's campaign on Sunday after having a meal with the candidate.
Signs had been pointing to Garcia’s endorsement of Lightfoot ever since the February election, as the candidate chose Garcia’s campaign manager Manny Perez to run her run-off campaign. Another close Garcia ally, Clem Balanoff, has also thrown support being Lightfoot, as the One Revolution Chicago group endorsed her on Friday.