In 1989, President George H. W. Bush appointed Hempstone ambassador to Kenya at a time when the United States was beginning to pressure African countries to democratize and improve human rights.

Hempstone worked toward these goals by advocating for multiparty elections in Kenya in 1991, nine years after Kenyan president Daniel arap Moi banned all parties except his own.

The Moi administration derided him, saying he failed to understand that strong, unified government was necessary to keep Kenya's tribal groups from dividing the nation.

Hempstone aided dissidents and befriended opponents of the Moi administration, causing the African press to describe his style as "bulldozer diplomacy."

In 2001, former Kenyan government minister Nicholas Biwott successfully sued Hempstone in High Court Civil Suit Case No.