Reinhart was born on September 15, 1893, in Polk, Ohio (pop. 250). He worked briefly as a rural school teacher, in North Red Haw, Ohio, until 1911. He entered the United States Military Academy (USMA) at West Point, New York, in 1912, graduating from there in June 1916, and was commissioned as a second lieutenant into the Field Artillery Branch of the United States Army at Fort Bliss, Texas. Fay B. Prickett, Robert B. McBride Jr., Horace L. McBride, William R. Woodward, Thomas Lyle Martin, Roland P. Shugg, Otto F. Lange, Louis E. Hibbs, Joseph M. Tully, Thomas D. Finley, William M. Hoge, Ludson D. Worsham, Dwight Johns, Calvin DeWitt Jr., Robert Neyland, Wilhelm D. Styer and James Joseph O'Hare, all of them destined to attain general officer rank, were among Reinhart's fellow graduates.

As aide-de-camp to Brigadier General Peyton C. March (who became Army Chief of Staff in 1918) Reinhart, promoted on May 15 to captain,^[1] sailed for France on June 30, 1917, almost three months after the American entry into World War I.^[2] After arriving on the Western Front, the main theater of war, in late 1917, he assumed command of Battery 'A' of the 17th Field Artillery Regiment, part of the 2nd Division of the American Expeditionary Forces (AEF), from February 12, 1918, to July 10, 1918 (in action during the defense of sector from March 21 to May 12, Battle of Bois de Belleau). Next, Reinhart commanded the 1st Battalion, 17th Field Artillery Regiment (Battle of Soissons, Ypres-Lys, and Meuse-Argonne). He commanded the battalion until the war ended on November 11, 1918, with the signing of the armistice with Germany. Reinhart was awarded the Army Distinguished Service Medal for his actions in combat during World War I.^[3] The citation for his Army DSM 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 Major (Field Artillery) Stanley Eric Reinhart, 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. In Command of a battery and subsequently a battalion of the 17th Field Artillery, 2d Division, Major Reinhart gave proof of high qualities of leadership and military attainments, notably during the operations near Soissons in July 1918, when he skillfully maneuvered his battalion in front of the infantry under machine-gun fire from the enemy with but few casualties to his command. Later he rendered valuable and loyal service as Chief of Staff of Artillery, 6th Army Corps.^[4][5]

On August 4, 1919, almost nine months after the war ended, Reinhart returned to the United States, where he married Jeannette Crane of Toledo, Ohio, on May 5, 1920, at West Point, New York. They had a son and daughter.

Between the wars he served three years as an instructor of field artillery tactics at the USMA;^[6] four years in the U.S. Army Command and General Staff School and the U.S. Army War College; two years as instructor at the U.S. Army Field Artillery School; three years General Staff with troops in Hawaii; and four years as Treasurer at West Point, New York. On July 1, 1937, he was promoted to lieutenant colonel,^[7] and again, almost four years later, to the temporary rank of full colonel on June 26, 1941.^[7] By this time he was serving in Hawaii as executive officer (XO) of the 8th Field Artillery Regiment, having been in this post since September 1940. Soon afterwards, however, Reinhart was made commanding officer (CO) of the 13th Field Artillery Regiment, then also serving in Hawaii.^[7]

As a temporary brigadier general from March 11, 1942,^[7] three months after the American entry into World War II, he commanded the artillery of the 25th Infantry Division, defending the shores of Oahu in the Pacific War. On December 6, 1942, Reinhart sailed for Guadalcanal to participate in operations that would ultimately help terminate hostilities there. Ordered home to the United States by the War Department on April 22, 1943, he landed at San Francisco, California on April 26.

From July 1, 1943, until December 18, 1944, Reinhart, who received a temporary promotion to the rank of major general on September 17, 1943 (and promoted to the permanent rank of colonel on August 1, 1944),^[7] organized and trained the 65th Infantry Division at Camp Shelby, Mississippi. He was aided by his Assistant Division Commander (ADC), Brigadier General Henry A. Barber until November when Brigadier John E. Copeland replaced him.

On January 10, 1945, as the Commanding General (CG) of the 65th, he, with his division, sailed to the European Theater of Operations (ETO). He joined Lieutenant General George Patton's U.S. Third Army at the Sarre River, and fought with it on the Western Front across Germany and Austria.

Under his leadership, the 65th Division managed forced crossings of the Fulda, Werra, Danube, Inn, Traun, and Enns Rivers. His soldiers took the German cities of Saarlautern, Neunkirchen, Oberursel, Friedberg, Hattenback, Bebra, Rottenburg (Bavaria), Treffurt, Langensalza, Neumarkt, Regensburg, and Passau—as well as Schärding, Eferding, Linz, and Enns in Austria. His men captured the German Danube Flotilla and the Hungarian Navy, consisting of 25 armed ships and over 400 other craft.

At the end of combat, Reinhart and the 65th Infantry Division were over 100 miles (160 kilometers) east of a north and south line through Berlin, Germany. Fighting in Europe was to end at midnight on May 8, 1945. By now a major general, Reinhart arrived in Erlauf, a hamlet in Austria, where he met the Soviets and shook hands with his counterpart. In addition to commanding his own troops, Reinhart was soon appointed as military governor of Upper Austria.^[7]

Reinhart continued to reside in Linz, where the 65th Infantry Division, and subsequently the 26th Infantry Division, had its headquarters.

Hospitalized on October 15, 1945, Reinhart returned to the United States as a patient on November 15, 1945. On September 30, 1946, he retired from the army after 30 years due to physical disability, with the rank of major general.^[7] He died in Hendersonville, North Carolina, on June 4, 1975, at the age of 81, and was buried at West Point Cemetery.^[8]

Stanley Reinhart received many military decorations during his career. He also became an honorary member of the Russian Guards.

Major General Reinhart's ribbon bar:

• 65th Infantry Division Association
• "Right to be Proud: History of the 65th Infantry Division's March Across Germany" (World War II unit history booklet published in 1945)
• Generals of World War II