Garre replaces Fabrizio Giordano, who is leaving Brazil to return to his native Italy, as managing director of the operation. She will report to Fabian Hernandez, chief executive officer of Millward Brown Latin America.
Hernandez said: "I am very excited to have Valkiria head our business in Brazil. I have worked with her for nine years and she is one of those rare talents that combine excellence in research with the ability to grow business."
Prior to joining Millward Brown nine years ago Garre, who is a chemistry graduate, worked at Unilever.