Mischief is sending out a team of three, led by head of sport Simon Bristow, to open the office for the start of the month-long tournament in June.
It is the first time the Engine-owned agency has set up outside the UK, in what has been described as a potential sign of things to come by Mischief CEO Frankie Cory.
"We will be in Brazil as a test and learn exercise and as part of looking to develop the Mischief brand globally," she said.
"The World Cup is just the beginning; over the next two years all eyes from around the world will be on Brazil, the potential goes way beyond sport. Brazil is an emerging market and this is a real opportunity to test, learn and explore, on the ground."
Cory, who will also fly out on a short-term basis to Rio, confirmed the agency was in talks with other clients about using the new set-up but declined to comment further.