Democratic Governor John Bel Edwards won the Louisiana governor’s election on Saturday evening after a tightly fought race.
The incumbent faced a strong challenge from Republican Eddie Rispone.
The result comes as a blow to President Donald Trump who backed his fellow Republican.
Mr Trump made two campaigning visits to the state in the past two weeks, turning the run-off election into a test of his own popularity.
On Saturday he posted several tweets urging people to vote for Mr Rispone.
Earlier this month, Republicans lost another gubernatorial race in Kentucky and Democrats seized full control of the legislature in Virginia.
The results are considered a gauge of the political mood ahead of next year’s presidential election.