Smuts was a supporter of Cecil Rhodes until it was revealed that Rhodes had instigated the fateful Jameson Raid by a group of Uitlanders on the Transvaal Republic. He moved from the Cape to practice law in Johannesburg where he became State Attorney. He later became a Minister in the Transvaal government led by Paul Kruger until the outbreak of the Boer War.
During the Boer War he led a Boer Commando in the Cape Colony and showed a great aptitude for guerrilla tactics. After the war ended in 1902 he returned to politics as a member of the government of the Union of South Africa led by Louis Botha until the outbreak of World War I when he rejoined the army. In 1917 he was invited to join the Imperial War Cabinet by David Lloyd George.
During World War II Smuts worked closely with Winston Churchill and attained the rank of Field Marshall. He was the only person who was a signatory to both the peace treaties ending the two world wars. He contributed to the formation of both the League of Nations and the United Nations.
He is remembered also for the coining of the terms holism and holistic: abstractions not unnaturally linked to his political concerns.
Johannesburg International Airport was formerly named after him.