[1] His younger brother Robert S. Garrett (1875–1961) became an American Olympic champion, as well as investment banker and archeological excavation philanthropist.

[1] In 1901, Garrett embarked on a diplomatic career with appointment as Secretary of the United States legation at The Hague.

Garrett and his wife, Alice Warder Garrett, entertained and patronized artists, filling the house with Tiffany lamps, paintings by Zuloaga, Pablo Picasso, Raoul Dufy, Degas and Amedeo Modigliani and a custom-designed stage by Leon Bakst.

On December 24, 1908, Garrett was married to Alice Warder (1877–1952),[20] who shared his love of the arts and travel.

[22] Garrett and several of his family members were well known collectors of rare books and manuscripts, coins and other items.

He donated his papers and much of his library to Johns Hopkins University, and many of his other items are still bought and sold by collectors.