The appointment of the Hull-born 49-year-old Keable will ease the financial burden previously borne by chairman Neil Hudgell and vice-chairman Rob Crossland, who last season threatened to walk away from the club unless new investment was secured.
Keable lives in the Astrakhan region of Russia, where he has business interests in the oil and gas industry.
"I've been a lifelong Rovers supporter, as have my family, and I'm fortunate enough to be in a position where I can make a contribution to the club financially," he said.
"It all came about through my daughter, who is an avid Rovers fan. She'd seen a piece in the local paper about the club seeking potential new investment and was straight onto me about getting involved.
"I spend the majority of my time in Russia but will certainly be trying to get to a few more games during the season."
Hudgell said: "It's been public knowledge for some time that we have been looking for additional investment so to have John joining the board of directors is good news for the club."