Arthur Gray Leonard (March 15, 1865 – 17 December 1932) was an American researcher, geologist and educator.

The first State Geologist of North Dakota, he was also a professor of geology at the University of North Dakota and made contributions to the knowledge of lignite coal and its relation to geologic time.

Before going to North Dakota in 1903, he served as assistant state geologist of Iowa, assistant professor of geology at the University of Missouri and professor of geology at Western College.

In the early morning of December 17, 1932, A. G. Leonard succumbed to the ill effects of a heart disease that had kept him at home since September.

The mineraloid Leonardite and a building on the campus of University of North Dakota are named after him.