John Mullan (31 July 1830- 28 December 1909) was a soldier, explorer and road builder.
Mullan was born in Norfolk, Virginia and graduated from West Point in 1852. He became a member of Isaac Stevens's party to explore the newly-created Washington Territory. Mullan was placed in charge of selecting a wagon route (now commonly called the Mullan Road) between Fort Benton (Montana) and Fort Walla Walla (Washington). Mullan, a topographical engineer, began gathering information in 1854.
Mullan was promoted to First Lieutenant in February 1855 and transferred to Florida for two years. He returned to Washington Territory, and from 1858 to 1862, was engaged as chief of construction in building the wagon road across the Rockies.
Mullan was promoted Captain in 1862 and married in 1863. He resigned to begin ranching near Walla Walla, an endeavor that failed. He opened a successful law practice at San Francisco, moved to Washington, D.C., in 1878, and died in that city in 1909. From 1883 to 1884, he succeeded General Charles Ewing as Catholic Commissioner for Indian Missions, (later the Bureau of Catholic Indian Missions), which involved defending Roman Catholic mission interests and the rights of Native Americans.