Ben Lear was born in Hamilton, Ontario on May 12, 1879. His military service began in 1898, when he enlisted with the 1st Colorado Infantry, USV, for the Spanish-American War as a First Sergeant. He was promoted to second lieutenant during the Philippine-American War in the 1st Colorado and later in the 36th Infantry, USV, but joined the regular army as a sergeant at the end of the war. He subsequently served in World War I.

He was promoted to Brigadier General in May 1936 and Major General in October 1938. He commanded the 1st Cavalry Division from 1936 to 1938, and the Pacific Sector of the Panama Canal Zone from 1938 to 1940. He was commanding general of U.S. Second Army from October 20, 1940 to April 25, 1943 and was promoted to temporary lieutenant general in October 1940. As such, he was responsible for training a large number of U.S. soldiers during World War II.

He became known as a strict disciplinarian. During the Louisiana Maneuvers, Lear led his U.S. Second Army against the U.S. Third Army under Lieutenant General Walter Krueger. In these maneuvers, Lear judged the control and discipline of the 35th Division to be unsatisfactory and relieved Truman of his command.

Lear did retire in May 1943, but was immediately recalled to active duty to serve on the Personnel Board of the Secretary of War, and promoted to Lieutenant General and later became Commanding General of Army Ground Forces.

After the German counter-attack in the Ardennes, caused a manpower crisis, he was appointed Deputy Commander of European Theater of Operations, US Army, responsible for Theater Manpower. As such, he overhauled the replacement system, but the war against Germany ended before the full benefits of his reforms could be realized. He retired again in July 1945, but was promoted to General on July 19, 1954 by special Act of Congress (Public Law 83-508).

He died on November 2, 1966. His Medals include the Distinguished Service Medal (2) and the Silver Star.