In doing so, Gates will serve as an advisor to longtime friend and Berkshire Hathaway CEO Warren Buffett.
In a statement, Gates said he hoped his years of experience at Microsoft would prove to be of value to Berkshire's shareholders.
"I am delighted and honored to have been asked to serve on the board of this very successful company," Gates said. Gates also serves on the board of Bothell, Wash.-based biotech company Icos.
Despite being close to Gates, Buffett has long eschewed investing in technology companies, concentrating much of his investment in the insurance business.
In 1997, top Microsoft Office executive Jeff Raikes sent Buffett an e-mail urging the billionaire to consider investing in Microsoft, noting the economic "moat" between Microsoft and its competitors was stronger than other Hathaway investments, such as Coca-Cola.
The e-mail came to light during a consumer class-action trial in Minnesota.
