Hühnlein was born in Neustädtlein, Upper Franconia the son of a teacher. He married his wife Paula (nee Däumling) in 1906 and the couple had three daughters, one of whom died in infancy.
He served in World War I, obtaining the rank of major. He had been decorated with the Iron Cross Second Class and First Class. After the war, he was a company commander in the Freikorps Epp from 1919 to 1920.
He first heard Adolf Hitler speak in the barracks of the Bavarian Life Guard Regiment in 1919. He was a member of Ernst Röhm’s anti-Semitic nationalist Bund Reichskriegsflagge (Imperial War Flag Society) until 1923.
He was involved in the Beer Hall Putsch—the unsuccessful attempt by Hitler and the NSDAP to seize power in Munich on 9 November 1923. He was held in investigative detention from November 1923 to March 1924 at Stadelheim, Neudeck and Landsberg Prison. He was discharged from the Reichswehr in March 1924, and was sentenced to six months’ incarceration at Landsberg for his role in the unsuccessful Putsch. There he joined Hitler and other conspirators. This event would set Hühnlein on a life of Nazi politics and he rose through the ranks after being released from prison.
He joined the Nazi Party in 1930 and served in the Sturmabteilung (SA). Ernst Röhm appointed him an SA-Obergruppenführer and by 1927, Hühnlein was head of the SA automotive engineering section.
Hühnlein was then appointed the leader of the National Socialist Automobile Corps (NSAK), which was to serve as a motorized corps of the SA. Thereafter, Hühnlein suggested the name be changed to National Socialist Motor Corps (NSKK). The name change became official on 1 May 1931. It was a paramilitary organization with its own system of paramilitary ranks and the smallest of the Nazi Party organizations. Under Hühnlein’s leadership, the NSKK membership rose rapidly, from 30,000 men in April 1933 to 350,000 in September 1933, after absorbing all of Germany’s private motor clubs. By 1939, there were 500,000 NSKK members.
The primary aim of the Corps was to educate its members in motoring skills and to transport NSDAP and SA officials/members. All race car drivers were required to become members of the NSKK. Hühnlein often presented the trophies at German Grand Prix races and made certain Nazi flags and bunting covered the victory tribunes. The most famous race car driver that had to answer to Hühnlein was Bernd Rosemeyer, who drove the Auto Union Silver Arrow. From 1935 onward, the NSKK also provided training for Panzer crews and drivers of the German Army. Through his relationship with Hühnlein, Heinz Guderian was able to ensure the training of Germany’s future tank and truck drivers, approximately 187,000 of them in the years 1933 to 1939.
Hühnlein was the NSKK Korpsführer from 30 April 1933 until his death in Munich on 18 June 1942. He was posthumously awarded the Party’s highest decoration, the German Order on 22 June 1942.