"I wanted somebody with fight. I wanted somebody with passion. I wanted somebody that had conviction to do the right thing, but I wanted somebody humble enough that remembers that you work for all the people,” she said Wednesday in Chapin, South Carolina.
In a CNN-ORC poll released Wednesday, Rubio garnered 14 percent support compared to 21 for Cruz and 37 for Trump.
Rubio said he was honored to have Haley’s support as she "embodies for me everything that I want the Republican party and the conservative movement to be about. Everything it is about."
Both Haley and Rubio played up veterans’ affairs and the need to rebuild the military while speaking Wednesday.
"I am a military wife of a combat veteran. I want a president who will have the backs of our military veterans and those in active duty," said Haley.
Overheard from a voter at Rubio/ Haley rally: "That's our ticket right there!" pic.twitter.com/ZOMB6rt9c6— Ines de La Cuetara (@InesdLC) February 17, 2016
They also drew parallels between their immigrant stories. Haley is the daughter of Indian immigrants; Rubio is the son of Cuban immigrants.
“I wanted somebody that was going to go and show my parents that the best decision they ever made for their children was coming to America," Haley said.
Haley thanked all candidates "for their sacrifice and their willingness to serve" -- but said her job was to find someone who would “go back to Washington, D.C. and bring a conscience back to our Republicans.”
Others had been courting Haley’s support, including former Florida Gov. Jeb Bush. He spoke with Haley earlier this week and sent his brother, former President George W. Bush, to court her personally when he was in the state.
"I'm disappointed," Bush told reporters Wednesday. "She's a very good governor and should I win the nomination, there will be a role for her in the campaign, trust me. She's a great person.”
Haley had said Tuesday she was still deciding who would snag her support. Rubio had already been endorsed by two other leading South Carolina officials: Sen. Tim Scott and Rep. Trey Gowdy.
ABC News' Tom Llamas contributed to this report.