James McDonald Gardiner (May 22, 1857 – November 25, 1925) was an American architect, lay Anglican church missionary and educator who lived and worked in Japan during the Meiji period.

As a lay missionary in the Anglican Church in Japan his connection with Bishop Channing Moore Williams and the work of US Episcopal Church mission was close, leading in part to his appointment as one of the first Presidents of St. Paul's School, the founding institution of Rikkyo University.

The three-story, red brick, school buildings in an American Victorian Gothic style were completed in 1881, but suffered significant damage in an earthquake in 1894.

Gardiner was also responsible for the design of adjacent Holy Trinity Cathedral, completed in 1890, which served as the center of Episcopal Church mission activity in the city.

[1] Other than St. Agnes Cathedral (Kyoto), other buildings of note designed by Gardiner and still preserved in Japan include St. John's Church, Kyoto (1907), now in the historic building collection at Meiji-mura, and the former residence of Sadatsuchi Uchida, known as The Diplomat's House (1910), since 1995 a feature of the Italian Garden park in Yamate, Yokohama.