The 49-year-old will replace Michael Barton who stepped down on March 2 following his departure from Pala Investments, Sierra's majority shareholder, to pursue other career opportunities.
Edwards has extensive experience in mining and investment banking, with a particular focus on the natural resources sector.
He is currently a Director of MMC Norilsk Nickel, GB MInerals and Highcross Resources Limited, and was previously a Senior Advisor to Royal Bank of Canada Capital Markets metals and mining investment banking division.
John Sisay, Sierra Rutile's chief executive, said: "On behalf of the executive team, I welcome Robert to his role on the board and I look forward to working with him.
"Robert's extensive knowledge of mining, emerging markets, in particular Africa, and equity capital markets will complement the management team as we continue to realise the full potential of Sierra Rutile's world-class asset."