The agreement includes an option to make the transfer permanent at the end of the campaign for the 21-year-old centre-back.
Smith joined QPR from Stellenbosch and has made limited first-team appearances in the Championship. The loan move will provide him with regular playing time in Major League Soccer as he continues his development.
The defender has already represented South Africa at both youth and senior levels, including featuring at the U-20 Africa Cup of Nations and the FIFA U-20 World Cup. New England Revolution will be hoping his pace, defensive reading and composure can strengthen their backline as they look ahead to the remainder of the MLS season.