"I was saddened to learn of Sir Brian's death and my thoughts are with his family at this time," he said.
"Sir Brian was a gracious and articulate politician who was always looking for solutions. He represented the best of the pragmatic tradition of the National Party."
Mr Key said Sir Brian had a truly international view of New Zealand's place in the world and was a strong advocate of the country's trade interests in a time of profound change.
Labour leader David Shearer expressed his condolences to Sir Brian's family, friends and former colleagues.
He described Sir Brian as a dedicated politician.
"He served his country with distinction and we thank him for his contribution. Our thoughts are with Sir Brian's family and friends at this very sad time.''