At the time when Henlein was growing up, Reichenberg was a center of tension between the long-established German community vs. newly arrived Czechs from the countryside who had come to work in the town's factories.
Henlein attended business school in Gablonz (Jablonec nad Nisou) and in World War I entered military service in the Austro-Hungarian Army as a military volunteer (Kriegsfreiwilliger), assigned to k.u.k. Tiroler Kaiser-Jäger-Regiment Nr. 3. In May 1916 he attended Officer Candidate School and then was assigned to k.u.k. Infanterie-Regiment Nr. 27 based in Graz. He saw Italian Front service in the Dolomites at Monte Forno, Mont Sief, and Monte Maletta from May 1916 to 17 November 1917.
Educated at a commercial college and employed as a bank clerk after military service during World War I (he was a prisoner of war in Italy until 1919), Henlein became the gym instructor of a Sudeten German club in Asch in 1925.
In 1931 he was appointed leader of the German Gymnastic Union in Czechoslovakia and in October 1933 he founded the Sudeten German Heimatfront (Patriotic Front) to replace the prohibited NSDAP.
Two years later it changed its name to the Sudetendeutsche Partei (SDP), demanding autonomy for the Sudeten German minority within the framework of the Czech State. In the elections of 1935 the SDP obtained forty-four seats and in effect represented over half of the German-speaking population of Czechoslovakia. Only the communists and Social Democrats refused to identify with its demands for full cultural autonomy and the transformation of Czechoslovakia into a federal State on the Swiss model.
From 1935 onwards, the SDP was secretly in receipt of subsidies from the Third Reich via the Volksdeutsche Mittelstelle (controlled by Werner Lorenz) and the German embassy in Prague, as well as being granted 15,0 marks a month from the Ausland Organization. As a fifth column the SDP played a key role in subverting the Czech State, enabling Hitler to manipulate the dispute between the Sudeten Germans and the Czech government from within. Gradually all regional and local organizations, sporting societies, cultural associations, choral and musical societies, etc., in the Sudetenland were infiltrated and transformed into Nazi cells.
Though Henlein continued to bamboozle the British with his denials that he had any connection with National Socialism or the Third Reich, by 1937 his Party was openly pro-Nazi and anti-semitic. At a secret meeting with Hitler after the annexation of Austria on 28 March 1938, Henlein and the Führer agreed on a common strategy based on the principle: ‘We must always demand so much that we can never be satisfied.' Henlein did not return to Czechoslovakia until it was already occupied by German troops as a result of the Munich agreements. Already an SS Lieutenant-General and member of the Reichstag, on 1 May 1939 he was appointed head of the Civil Administration in the Sudetenland and Gauleiter of the region, positions he held until the end of World War II.
In June 1943 the Reich Governor of the Sudetenland was promoted to SS-Obergruppenfiihrer. Following capture by the Americans, Henlein committed suicide in an Allied POW camp in May 1945.