The drinks group has appointed Stewart as an independent non-executive director and chairman designate.
He will take over from current chairman Tony O'Brien, who is retiring later this year.
O'Brien has held the role of chairman for eight years, following 20 years as chief executive.
Stewart will officially take up the role as non-executive chairman at the group's annual general meeting on August 5.
“We are delighted to have attracted someone of Sir Brian's calibre to the C&C Group board, and that he has accepted the role to become chairman,” said O'Brien.
“With his vast knowledge and experience of the LAD sector, coupled with his valuable trade connections, he is well equipped to provide astute strategic leadership of the board, and is the ideal person to lead the next phase of C&C's development.”
Stewart was chief executive and then chairman of S&N and oversaw its expansion across Europe, India and China, including the takeover of Kronenbourg in France.
C&C said he was “instrumental” in the acquisition of Bulmer of Hereford.
Stewart said: “C&C Group has an attractive business, a strong portfolio of brands and an experienced team. I look forward to joining the board and contributing to the continuing success of the business. Tony and the team have
built strong brands and developed real growth opportunities, and the company clearly has exciting potential.”