The rare endorsement from Obama, who has often stayed away from contentious Democratic primary fights, will likely boost Schatz in his tough race against Rep. Colleen Hanabusa, who is challenging him for the party's nomination.
"I have worked with Senator Schatz on the issues that matter to Hawaii,” said Obama, in a statement posted on Schatz's website. “Brian's deep commitment to the people of Hawaii and his effective leadership are why I believe it is important to return him to the Senate.
“Senator Schatz is protecting Hawaii's values and fighting every day on behalf of middle-class families,” added the president. “There is no question that Senator Schatz is the right choice to continue delivering for Hawaii."
"I'm incredibly honored to receive President Obama's endorsement," tweeted Schatz.
Schatz was an early supporter of Obama, who was born in Hawaii and has maintained close ties there. The president and his family regularly spend their Christmas holidays on the islands.
Schatz was appointed by Democratic Gov. Neil Abercrombie to fill the seat held by former Sen. Daniel Inouye, D-Hawaii, who died in December 2012.
Before his death, though, Inouye in a letter to Abercrombie asked that Hanabusa be his successor.
A February poll showed the two Democratic contenders in a dead heat with 40 percent support each.