A multi-million dollar transformation of the 220-room hotel was directed by designer Adam D Tihany, who took Edward Lutyens' modernist vision as his inspiration, Oberoi Group said in a statement.
The renovation was expected to take two years but was completed three months ahead of schedule, it added.
Oberoi Group Executive Chairman P R S Oberoi termed it a significant moment for the Group.
"When my late father Rai Bahadur M S Oberoi opened the hotel in the autumn of 1965, he wished it to be the most modern luxury hotel. I am confident that The Oberoi, New Delhi will continue this tradition," he said.
The Group is also engaged in flight catering, managing airport restaurants, travel and tour services, car rentals, project management and corporate air charters.