Politically, Reinthaller initially belonged to the Landbund before switching to support the Nazis in 1928. He rose through the ranks of Austria's Nazi set-up, becoming state peasant leader in 1934, although his moderate stance, particularly with regards to the use of violence, meant that he was often in conflict with Theodor Habicht who feared that Reinthaller was preparing to break away and form a specifically Austrian Nazi movement that would reject union with Germany. However Habicht did not move against Reinthaller, who enjoyed good personal relations with Rudolf Hess and Richard Walther Darré, although ultimately he was removed after he spearheaded his own negotiations with Engelbert Dollfuß. Although he had no real involvement in the failed Nazi putsch of July 1934 Reinthaller was nonetheless held for a while in Kaisersteinbruch concentration camp where he met and befriended Ernst Kaltenbrunner who, despite his own more radical views, became a supporter of Reinthaller. Reinthaller attempted to negotiate an agreement with Kurt Schuschnigg with a view to the Nazis entering the Vaterländische Front although when this failed he stepped aside from his role as the effective leader of Austria's Nazis in favour of Hermann Neubacher. Reinthaller stepped away from active politics after this, although he remained a voice of dissent on the sidelines, attacking nazi anti-Semitism on the basis of its negative impact on international opinion of the Nazis, whilst also resisting any move to complete Anschluss. He would re-emerge in 1935, with the backing of Kaltenbrunner and Franz Langoth, to form a National Front that sought to unite Austria's Sturmabteilung and Schutzstaffel with other rightist groups in the service of the Vaterländische Front. However the radical Nazi leaderJosef Leopold stepped in as he felt Reinthaller was diluting the impact of Austria's Nazis too much and had him deprived of his party positions in 1937.
Along with Rudolf Neumayer and Guido Schmidt, Reinthaller was brought before the Austrian People's Court and accused of "high treason against the Austrian people", with the three labelled as being those most responsible for the Anschluss. Reinthaller was found guilty of lesser charges and sentenced to three years imprisonment, serving the sentence from 1950 when he was released from American custody. After the war, Reinthaller became an advocate of the 'Third force' in Austrian politics. On this basis he was chosen to lead the FPÖ when it replaced the Federation of Independents in 1956. Before long Reinthaller once again became an important figure in Austrian politics as, despite his Nazi origins, Julius Raab made a deal with Reinthaller in 1957 that he would ensure that the FPÖ did not nominate a candidate for the Presidency. As a result, Raab was thus nominated as a joint Austrian People's Party-FPÖ candidate. He died in Innviertel in 1958, with the leadership of the FPÖ passing to Friedrich Peter.
