Ogilvy declined to comment on whether it had acquired a minority or majority stake in the agency.
It said it is now looking seriously at Myanmar [formerly known as Burma] as a new growth market and said there could be further announcements in the months ahead.
Paul Heath, CEO of Ogilvy Asia-Pacific, said Today Advertising had a "great reputation" in Myanmar.
He said: "We believe they are the perfect partner to work alongside us and our clients as the business potential of Asia’s newest frontier becomes apparent."
John Goodman, regional president of Ogilvy Action Asia-Pacific, who led negotiations for Ogilvy, said: "Myanmar is important because it has a population of 56 million people, abundant natural resources and sits at the crossroads between China, India and Southeast Asia.
"In colonial times, it was the most prosperous country in South-East Asia. It's highly unusual for a new market of this potential to suddenly open up."