I will cite Hugo Ott, writer of an objective biography,  Martin Heidegger:unterwegs zu seiner Biographie (1988).  Further, J.P Stern’s review of Ott’s book in the London Review of Books (20 April 1989) will be useful. 

Hugo Ott shows that Heidegger’s involvement with the Nazi Party was never reluctant, never as a mere fellow-traveler, nor even as Karl Jaspers wrote in 1945, as a “non-political, childish scholar over his head.”  

Rather -- Heidegger became Rector of Freiburg University on 22 April 1933 ten weeks after Hitler’s assumption of power, not as a surprise promotion as he had claimed -- but with Nazi Party collusion, deliberately orchestrated.  His long-term promise was to become the fuhrer of Germany’s University system, and to introduce reforms so that all German Universities would step along with the Nazi Party.. 

Heidegger openly stated his goal to serve, “the forces and demands of the National Socialist State.”  He had joined the Nazi Party with plenty of fanfare in 1933, and he paid his dues to the very end of the Third Reich. 

From Being and Time (1927) onward, Heidegger’s philosophical program promised to return to... 

......the single question of the essence of Being…Do we in our time have an answer to the question of what we really mean by Seiend? …What do we mean by saying that there are Things, or ‘entities of being’, in-the-world? (Heidegger, 1927)

And also (from his Introduction to Metaphysics, 1953): 

Heidegger, says Stern, acted as though the actual, political, social, intellectual, cultural and material situation of Adolf Hitler’s rise power provided the correct and unique Sitz Im Leben in which Philosophy through Heidegger could eventually solve ‘the question of German Being.  Two documents by Heidegger most clearly illustrate his ambition: 

(1) Heidegger's Inaugural Address as Rector of Freiburg University.   This addressed the student’s duty of service in (a) the Labor Corps; (b) the Army; and (c) academics – conveyed as a military duty.  He used the language of danger, distress, force, breeding, dire need, heroism, a last-ditch stand, and resolve in the face of Infinite Fate..  He borrowed freely from the biography of Hermann Goering – a common source of Nazi ideology.  As the winter session began, Heidegger addressed his students with these additional words: 

Stern writes: “Italicizing his verb, ‘ontic,’ Heidegger leaves no doubt about the metaphysical legitimacy of the Fuhrer’s, and thus also of his own, mission.”  

(2) Heidegger’s declaration of loyalty and support for Hitler.  He declared this nationwide on the day before the Nazi landslide referendum of 12 November 1933: 

Heidegger added later, that Sieg Heil! should be understood, not as a sign of allegiance to the Nazi Party, but as the national greeting of the New German Folk.  I say Stern is correct – this rhetoric obviously identifies Heidegger’s quasi-ontology with Hitler’s politics..

Finally, I turn to Heidegger’s only tome, his Being and Time (1927) in section I-IV, Being-in-the-world, and Being-with, and Being-Oneself – the “They”.  He claims that our Being-in-the-world is inauthentic when it appeals to ‘the average’ and ‘the everyday’, as summed up in the phrase, ‘they say.’ 

We take pleasure and enjoy ourselves as THEY take pleasure.  We read, see and judge about literature and art as THEY see and judge.  Likewise we shrink back from ‘the crowd’ as THEY shrink back.  We find ‘shocking’ what THEY find shocking…This…prescribes the mode of Everyday Being.  (Heidegger, 1927, Being and Time, tr. MacQuarrie, p. 164)   

According to J.P. Stern, Heidegger here describes his contempt for his contemporary intelligentsia.  Stern calls this, “the most demeaning political actualization.”  Heidegger poses this arrogance as a necessary stage on the road to salvation, namely, a new, national togetherness, promised by Hitler and the Nazi Party.