McGregor made a surprise appearance and announced the show Friday night at the D23 Expo in Anaheim, Calif.
Recent media reports said the actor was in negotiations to star as his iconic character in a standalone series for the streaming service, but neither Disney nor McGregor commented on the potential project until D23.
No other casting or premiere date were announced. Disney+ is slated to launch in November.
McGregor, 48, played the role of Obi-Wan in the Star Wars blockbusters The Phantom Menace, Attack of the Clones and Revenge of the Sith.
The late Alec Guiness played the hero as an older man in A New Hope, The Empire Strikes Back and Return of the Jedi.
McGregor's other credits include Season 3 of Fargo, as well as the films Christopher Robin, Beauty and the Beast, Big Fish, Moulin Rouge, Black Hawk Down and Trainspotting.
He will soon be seen in The Shining sequel, Doctor Sleep.