His father, Mark Mayo Boatner, graduated from Virginia Military Institute and was a respected lawyer and judge in New Orleans.

He was one of six children: Mark II, Frank, Haydon, Bryant (who became an Air Force Lieutenant general,[2] Charlotte and Elizabeth (Betty).

He enlisted in the United States Marine Corps near the end of World War I but did not complete training in time to deploy.

From 1930 to 1934 he served as assistant military attaché at the American Embassy, Peking, and during this time he became fluent in Mandarin Chinese.

He was appointed as commanding officer of the forward echelon in Burma in 1942 and was promoted to brigadier general in November 1942.