It wasn't immediately clear how much Haley's endorsement would benefit Rubio - but normally the backing of a sitting Governor is one of the biggest prizes any candidate can get in a race for President, since it opens doors in that state.
Both Rubio and Haley are 44 years old - both rising stars within the Republican Party.
Will her endorsement matter? Rubio already has the backing of Sen. Tim Scott (R-SC) and Rep. Trey Gowdy (R-SC), both of which also give him a little extra in the Palmetto State.
We will see on Saturday if those endorsements carry any weight at the polls.