He quit Ibrox in April amid allegations of having links with Craig Whyte, the discredited former owner of the Glasgow club.
However, Green strenuously denied any wrongdoing at the time of his resignation.
An independent investigation commissioned by the Rangers' board subsequently found no evidence Whyte had invested in the current Ibrox set-up.
Green had spearheaded a consortium during the summer of 2012 to purchase the business and assets of the club following liquidation after several months in administration.
A brief statement from Rangers to the Stock Exchange read: "The board of Rangers is pleased to announce it has appointed Charles Green as a consultant to the company.
"Mr Green's role will be to promote the interests of Rangers Football Club, specifically assisting with shareholder relations and advising the company on its capital structure."