FORMER cabinet secretary in John Howard's coalition government Michael L'Estrange is joining the board of mining giant Rio Tinto.

Rio Tinto chairman Jan du Plessis said Professor L'Estrange brought a wealth of expertise in foreign policy, international relations and trade to the board.

Professor L'Estrange, who will join Rio Tinto's board on September 1, was also secretary of the Department of Foreign Affairs and Trade from 2005 to 2009.