The U.S. President,
Obama made this known in a video he posted to Clinton's website after she secured the Democratic Party's nomination within the week.
"I'm with her, I am fired up and I cannot wait to get out there and campaign for Hillary", Obama said in the video.
He had been reluctant to jump into the race until the party's nomination was settled.
Spokesman Josh Earnest had repeatedly deflected questions about when an endorsement would come.
Clinton's rival Bernie Sanders met with Obama at the White House earlier on Thursday about the path forward for his campaign.
Sanders said on Tuesday after the meeting that he would continue to campaign through the primary in the U.S. capital.
He stopped short of endorsing Clinton, but said he will meet with her in the coming days and vowed to do everything he can to defeat Republican candidate Donald Trump.
Clinton on Tuesday declared herself the party's presumptive nominee after reaching the number of delegates needed to be named its standard-bearer in November elections.