In 1918, after the American entry into World War I, he was appointed a colonel in the National Army and in August of the same year was promoted to brigadier general.

The citation reads: The President of the United States of America, authorized by Act of Congress, July 9, 1918, takes pleasure in presenting the Army Distinguished Service Medal to Brigadier General Preston Brown, United States Army, for exceptionally meritorious and distinguished services to the Government of the United States, in a duty of great responsibility during World War I.

As chief of Staff of the 2d Division, General Brown directed the details of the battles near Chateau-Thierry, Soissons, and at the St. Mihiel salient with great credit.

[5] Brown retired to Martha's Vineyard, Massachusetts in 1936, having reached the rank of major general.

[3] Order of Battle of the United States Land Forces in the World War.