The purchase adds New Zealand, Sri Lanka and Bangladesh to its offer.
TNS chief executive, Mike Kirkham, said: "TNS and NFO have small offices in a lot of markets. By bringing the two together, we will have the capability to bolster our offering."
He pointed to a research panel in the US consisting of three million people, who participate in regular online polls. "Our size previously didn't allow us to do anything like this in Asia given the large investment needed. But now this can be made a more economical proposition," he said.
"The reason for the acquisition was not to take costs out. We're doing it to grow the business. NFO has skilled people and it will be these people who will drive us forward."