(Adds comment from SAB, critic)
LONDON, Aug 6 (Reuters) - Rio Tinto Chairman Jan duPlessis will become an independent non-executive director ofbrewer SABMiller Plc next month, with plans to becomechairman next year.
Du Plessis, 60, will join the brewer's board on Sept. 1 andwill succeed John Manser as chairman following its annualshareholder meeting in July 2015, the company said on Wednesday.
Du Plessis said he would like to continue serving aschairman of Australian mining giant Rio Tinto following theappointment, though he plans to step down from the board ofretailer Marks and Spencer Group, where he is currentlya director, in the first half of 2015.
Given the size of the two FTSE 100 companies, some criticsquestioned whether one man could effectively serve both roles.
"We're puzzled why the company would think someone whoalready has a very complex role as chair of one of the largestdiversified resource companies in the world could effectivelyalso chair SAB, and more effectively than anyone else," saidAndrew Whiley, spokesman for PIRC, a shareholder advisory firm.
PIRC generally opposes multiple chairmanships, Whiley said.
A spokesman for SABMiller, the world's second-largestbrewer, said it was "not unusual for board members to havemultiple roles on companies and other outside commitments".
"Jan will spend as much time as is necessary to fulfill hisduties as chairman," said the spokesman, Richard Farnsworth.
SABMiller shares were down 2 percent at 3,150 pence by 0956GMT, while Rio Tinto shares were roughly flat. (Reporting by Martinne Geller; Editing by Jason Neely and MarkPotter)