Hinda Gharbi and Jennifer Nason will join the board from March 1, while Ngaire Woods CBE will join on September 1.
Gharbi, who has dual Australian-Tunisian nationality, is executive vice president of reservoir and infrastructure at Schlumberger.
Adelaide-born Nason is a global chair at JP Morgan, based in New York.
Dual New Zealand and British citizen Woods, a professor of global economic governance at Oxford University, is the founding dean of the Blavatnik School of Government and a visiting lecturer at Harvard University.
Rio said new directors broadened the experience of the board, bringing complementary skills and international expertise across diverse backgrounds in natural resources, finance, technology, governance and public policy.
"I am delighted to welcome Hinda, Jennifer and Ngaire and look forward to benefiting from their insights and expertise in natural resources, finance, technology, governance and public policy," Rio chairman Simon Thompson said.
"Their diverse international experience will further strengthen the Rio Tinto board."
Rio previously had nine directors, with only one female, Megan Clark AC.
Dame Moya Greene stepped down in June 2019 after less than a year on the board.
The new appointments take Rio's board back to "full strength" with 12 directors, comprising eight men and four women.