It is understood he had been battling illness.
Buchanan joined the board in 2003 and was the senior independent director of BHP Billiton plc.
BHP Billiton chairman Jac Nasser paid tribute to Buchanan.
“Sir John provided wise counsel to his fellow directors and to management, and made an invaluable contribution to BHP Billiton,” he said.
“We have lost a highly respected and esteemed colleague who was greatly admired by those who worked with him.”
New Zealand-born Buchanan was a former chief financial officer of BP, where he spent most of his career.
The 72-year-old was formerly the deputy chairman of Vodafone Group and the former chairman of ARM Holdings and Smith & Nephew in the UK.
