Show producers Craig Zadan and Neil Meron announced DeGeneres' selection Friday. The movie awards show will air on ABC on March 2.
"There are few stars today who have Ellen's gift for comedy, with her great warmth and humanity," the producers said in a statement. "She is beloved everywhere."
DeGeneres quipped: "I am so excited to be hosting the Oscars for the second time. You know what they say - the third time's the charm."
She also announced the gig on Twitter, posting: "It's official: I'm hosting the #Oscars! I'd like to thank TheAcademy, my wife Portia and, oh dear, there goes the orchestra."
Last year's host, "Family Guy" creator Seth MacFarlane, drew mixed reviews for an edgy performance that included a song-and-dance number, "We Saw Your Boobs," about actresses who had gone topless on screen. He had already taken himself out of the running for a return engagement next year.
Academy Awards organizers had hoped to attract a younger audience with MacFarlane, and the ratings showed they succeeded.
With DeGeneres, they went for a star that Hollywood and television viewers were familiar and comfortable with.
About her first hosting role in 2007, television critic Frazier Moore of The Associated Press wrote that "like her, the evening was easygoing, comfortable and relatively unsurprising."
DeGeneres was nominated for an Emmy Award for her last gig. Her daytime talk show has won 45 Daytime Emmys during a decade on the air.
The Oscars, with 40.3 million viewers this year, is very often the year's most-watched television event after the Super Bowl.