Gardiner's essays, written in the tradition of Charles Lamb and William Hazlitt, found charm and philosophy in ordinary subjects—hats, handshakes, umbrellas, and everyday human follies. His light touch, irony, and humane insight made him one of the most popular essayists of the early twentieth century.
His principal collections include Prophets, Priests, and Kings (1908), Pillars of Society (1913), Pebbles on the Shore (1916), Leaves in the Wind (1918), Certain People of Importance (1922), and Many Furrows (1924). He also wrote political and biographical works such as The War Lords (1915). His essays remain anthologized classics of English prose.