He became a member of the parliament of Transvaal in 1897 and was a general during the Boer War. He later worked towards peace with the British, becoming Prime Minister of Transvaal in 1907, and Prime Minister of South Africa in 1910.
After the First World War started, he planned to send troops to take German South West Africa, a moved unpopular among Boers, which provoked the Boer Revolt. He argued that the terms of the Versailles Treaty were too harsh on the Central Powers, but signed the treaty anyway.