Harold Arminius Miller was born on December 9, 1875, in Menomonie, Wisconsin. His entry into the automotive world came through the short-lived Yale Automobile Company, after which he moved to Lansing, Michigan, to work as a race mechanic for Ransom E. Olds at Oldsmobile during the early Vanderbilt Cup races. Following an unsuccessful 1906 race season, Miller relocated to Los Angeles, California, where he opened a small machine shop that specialized in carburetor production.
Miller's carburetors became a commercial success, and by the 1910s his carburetor business was reportedly generating revenues of around one million dollars per year. His work on induction systems brought Miller into contact with the racing world more directly, and he began repairing and eventually building his own race cars. Among his technical contributions from this period were the development of aluminum pistons, aluminum alloys later adopted broadly in engine development, and the first carburetors and induction systems to employ Helmholtz resonators.
In the early 1920s, Miller designed a 3.0-litre four-cylinder engine drawing on lessons learned from Duesenberg and Peugeot powerplants that had passed through his shop for service. The engine used dual overhead camshafts and four valves per cylinder — an advanced specification for the era. Backed financially by Tommy Milton, the engine first proved itself in Jimmy Murphy's hands when Murphy drove a Duesenberg fitted with Miller's engine to victory in the 1922 Indianapolis 500.
Miller then developed complete single-seater race cars around supercharged 2.0-litre and 1.5-litre versions of his engine. Between 1923 and 1928, Miller-engined cars accounted for 83 percent of the Indianapolis 500 starting fields. The cars themselves won Indianapolis in 1926 and 1928, with his engines powering the winning machine in numerous other editions. A total of twelve Indianapolis 500 victories are directly attributed to Miller engines across all chassis combinations — nine in Miller-built cars, three in cars built by others using his powerplants.
Beyond the oval tracks, Miller engines also powered speedboats to race victories and world water speed records during the same period, including victories for the renowned Gar Wood.
Despite the on-track success of his products, Miller's business collapsed. He declared bankruptcy in 1933. His shop foreman and chief machinist, Fred Offenhauser, purchased the business and continued developing the engine under the Offenhauser name. The Offenhauser engine went on to dominate American oval racing through the 1970s, making Miller's original design one of the most influential powerplants in the history of motorsport.
After bankruptcy, Miller partnered with Indianapolis 500 enthusiast Preston Tucker. Together they formed Miller and Tucker, Inc., which in 1935 accepted a commission from Henry Ford to build ten modified Ford V-8 racers. Insufficient development time meant all ten retired from the 1935 Indianapolis 500 when steering boxes installed too close to the exhaust overheated and locked up. Privateers later refined the concept, and Ford-based Miller-Tucker cars continued running at Indianapolis through 1948.
Miller and Tucker also worked on military vehicle concepts in the late 1930s, developing the Tucker Combat Car — a light armored vehicle capable of 115 mph on pavement — and attempting unsuccessfully to sell it to the Dutch and American governments. The power-operated gun turret developed for this project was subsequently adopted for use in the B-17, B-29, PT boats, and landing craft. Miller's work with Tucker also brought chief mechanic John Eddie Offutt into the orbit of the future Tucker Sedan project.
Miller died on May 3, 1943, at Grace Hospital in Detroit, Michigan, aged 67.
Harry Miller's technical influence extended far beyond his own bankruptcy and death. The engine he designed in the early 1920s formed the direct lineage of the Offenhauser, which remained a force at Indianapolis until the 1980s — a competitive lifespan of nearly sixty years from its origins. His work on aluminum alloys and induction systems influenced engine manufacturing broadly. He was inducted into the Motorsports Hall of Fame of America in 1999 and the Automotive Hall of Fame in 2003.