Winger Merritt, 27, and 26-year-old five-eighth Sutton, have both signed three-year deals.
Between them, the pair have made over 300 NRL appearances since joining as juniors.
Rabbitohs CEO Shane Richardson is happy to have both Merritt and Sutton commit to the Club for a further three years.
“Both Nathan and John have been mainstays of our NRL side for many seasons and we’re proud to be able to make them both 10-year players at our Club with these contract extensions,” Mr Richardson said.
“Nathan has a fantastic try scoring record, in the top five of all time at this famous Club. John has sublime skills and has performed strongly at five-eighth, lock and centre for us over the past seven seasons.
“These guys are products of the South Sydney juniors and we’re pleased to have them in our squad alongside other juniors such as Eddy Pettybourne, Shannan McPherson, Jason Clark, Nathan Peats, James Roberts, Fetuli Talanoa, Beau Falloon, Kane Morgan and Adam Reynolds.”