Robert Lansing was born on October 17, 1864, in Watertown, New York. He attended Amherst College, graduating in 1886, before becoming a lawyer in his father's practice.

Lansing entered the world of diplomacy when his father-in-law, Secretary of State John Foster, brought him along to the Bering Sea Fur Seal Arbitration; Lansing himself would serve as private counsel for the Chinese and Mexican diplomatic delegations. In 1906, Lansing founded the American Society of International Law. and with it, the American Journal of International Law. Four years later, and despite Lansing's affiliation with the Democratic Party, President William Howard Taft named him U.S. counsel for the North Atlantic Coast Fisheries Arbitration Panel at The Hague.

Having been appointed counselor to the Department of State by President Woodrow Wilson in 1914, Lansing took over as secretary of state in June 1915 following the resignation of William Jennings Bryan. Though he was cut out of negotiations involving the House-Grey memorandum, Lansing would be involved in various initiatives, including interventions in Haiti, the Dominican Republic, and Russia. Wilson asked for his resignation following Lansing's convocation of a cabinet meeting -- without Wilson's approval -- during the period in which Edith Wilson presided over her husband's affairs.

Lansing left the cabinet on February 13, 1920. Thereafter, he would write two books: The Peace Negotiations: A Personal Memoir, and The Big Four and Others of the Peace Conference. Robert Lansing died in Washington, D.C., on October 30, 1928.