Hildebrand is an Intentionalist on the origins of the Holocaust question, arguing that the personality and role of Adolf Hitler was a crucial driving force behind the Final Solution. Writing in 1979, Hildebrand stated "Fundamental to National Socialist genocide was Hitler's race dogma...Hitler's programmatic ideas about the destruction of the Jews and racial domination have still to be rated as primary and causative, as motive and aim, as intention and goal of the "Jewish policy" of the Third Reich. Working closely with Andreas Hillgruber, Hildebrand took the view that such events as the Shoah and Operation Barbarossa were all the unfolding of Hitler's master plan. Along similar lines, in a 1976 article, Hildebrand commented on left-wing historians of the Nazi Germany that in his view they were "theoretically fixed, are vainly concerned with functional explanations of the autonomous force in history and as a result frequently contribute towards its trivialization. Hildebrand argued that the distinction drawn by the functionalists between the Einsatzgruppen massacres of Jews in the German-occupied parts of the Soviet Union in 1941-42 and between the rest of the Shoah is largely meaningless. Hildebrand wrote that "In qualitative terms, the executions by shooting were no different from the technically more efficient accomplishment of the 'physical final solution' by gassing, of which they were a prelude. In 1981, the British Marxist historian Timothy Mason in his essay 'Intention and explanation: A current controversy about the interpretation of National Socialism' from the book The "Fuehrer State" : Myth and reality coined the term "Intentionist" as part of an attack against Hildebrand and Karl Dietrich Bracher, both of whom Mason accused of focusing too much on Hitler as an explanation for the Holocaust.
Through Hildebrand is a leading advocate of the totalitarianism school and rejects any notion of generic fascism as intellectually inadequate, he does believe that the Third Reich was characterized by what he deems “authoritarian anarchy”. However, Hildebrand believes in contrast to the work of Martin Broszat and Hans Mommsen that the “authoritarian anarchy” caused by numerous competing bureaucracies strengthened, not weakened Hitler’s power. In Hildebrand's opinion, the "Hitler factor" was indeed the central causal agent of the Third Reich. Hildebrand has argued against the Sonderweg view of German history championed by the Mommsen brothers.
In the 1970s Hildebrand was deeply involved in a rancorous debate with Hans-Ulrich Wehler over the merits of traditional diplomatic history versus social history as way of explaining foreign policy. Together with Andreas Hillgruber, Hildebrand argued for the traditional Primat der Aussenpolitik (Primacy of Foreign Policy) approach with the focus on empirically examining the foreign policy making elite. Wehler by contrast argued for the Primat der Innenpolitik (Primacy of Domestic Politics) approach which called for seeing foreign policy largely as a reflection of domestic politics and employing theoretically-based research into social history to examine domestic politics. Another area of difference between Hildebrand and his left-wing critics in the role of geography in German history. Hildebrand has argued that Germany's position as the "country in the middle" bordered by Russia and France has often limited the options of the German government in the 19th-20th centuries.
In regards to the Globalist-Continentalist debate between those argue that the Hitler's foreign policy at world conquest against those who argue that Nazi foreign policy aim only at the conquest of Europe, Hildebrand has consistently taken a Globalist position, arguing that the foreign policy of the Third Reich did indeed have world domination as its goal, with Hitler following a Stufenplan (stage-by-stage plan) to reach that goal. In Hildebrand’s opinion, Hitler’s foreign policy aimed at nothing less then world conquest in his own lifetime, and those who argue otherwise are seriously misunderstanding the full scope of Hitler’s ambitions. Hildebrand sees Hitler's “Programme” for world domination as comprising in an equal measure crafty power politics and fanatical racism. Together with Andreas Hillgruber and Gerhard Weinberg, Hildebrand is considered to be one of the leading Globalist scholars. Through Hildebrand does not maintain that Hitler was a free agent in foreign policy, and accepts that there were structural limitations upon Hitler's room to manoeuvre, he contends that these limitations only had the effect of pushing Hitler into the direction that he always wanted to go. However, Hildebrand does not favor an exclusively Hitlerist interpretation of German foreign policy in the era of the Third Reich. In Hildebrand's view, there were three other fractions within the NSDAP who advocated foreign policy programmes different from Hitler's. One fraction, whom Hildebrand dubs the "revolutionary socialists", supported an anti-Western policy with support for independence movements within the British Empire and an alignment with the Soviet Union. Most closely associated the Strasser brothers, Gregor and Otto the "revolutionary socialist" fraction played no important role in the foreign policy of the Third Reich. A rival fraction whom Hildebrand calls the "agrarians" centered around the agrarian leader Richard Walther Darré, the Party "race theorist" Alfred Rosenberg and the Reichsfũhrer-SS Heinrich Himmler, favored an anti-industrial and anti-urban "blood and soil" ideology, expansion at the expense of the Soviet Union in order to acquire Lebensraum, alliance with Britain and opposition to the restoration of overseas colonies as threatening German racial purity. Another fraction, who Hildebrand refers to as the Wilhelmine Imperialists and whose leading personality was Hermann Göring, advocated at minimum the restoration of the borders of 1914 and the overseas empire, an zone of influence for Germany in Eastern Europe, and greater emphasis on traditional Machtpolitik as opposed to Hitler's racist vision of an endless and merciless Social Darwinist struggle between different "races" for lebensraum. Through the emphasis on the restoration of German colonies implied an anti-British policy, but in general, the Wilhelmine Imperialists were cautious about the prospect of war with Britain, and preferred to restore the pre-1914 German colonial empire through diplomacy rather than war. Of the three fractions, it was the "agrarians" whose views were most closest to Hitler's programme, but Hildebrand argues that there was an important difference in that the "agrarians" saw an alliance with Britain as being the natural alignment of two "Aryan" powers, whereas for Hitler the proposed British alliance was more a matter of power politics.
Since 1982, Hildebrand has worked at the University of Bonn as a professor in medieval and modern history, with a special interest in the 19th and 20th centuries. Hildebrand’s major work has been in diplomatic history and the development of the nation-state. He served as editor of the series concerning the publication of the documents of German foreign policy. In the mid-1980s, Hildebrand sat on a committee together with Thomas Nipperdey and Michael Stürmer in charge of vetting the publications issued by the Research Office of the West German Ministry of Defence. The committee attracted some controversy when it refused to publish a hostile biography of Gustav Noske.
In the Historikerstreit (historians' dispute) of the 1980s, Hildebrand sided with those who contended that the Holocaust, while a major tragedy of the 20th century was not a uniquely evil event, but just one out of many genocides of the 20th century. Furthermore, Hildebrand argued that the crimes of Joseph Stalin were just as evil as those of Adolf Hitler. In Germany, Hildebrand is well known for his disputes with the Mommsen brothers, Hans and Wolfgang over how best to understand Nazi Germany, especially evident at a conference held at the German Historical Institute in London in 1979 which resulted in numerous hostile exchanges. As one of the historians who more or less supported Ernst Nolte in the Historikerstreit, many feel his reputation has been somewhat damaged in the public eye. At first, Hildebrand praised Nolte's 1986 article Vergangenheit, die nicht vergehen will ("The Past That Will Not Go Away") as "path-breaking", but as the controversy caused by the Historikerstreit increased, Hildebrand increasingly wrote less and less in support of Nolte and more in the favour of his mentor Andreas Hillgruber. In a 1986 review of Nolte's essay "Between Myth and Revisionism", Hildebrand aruged Nolte had in a praiseworthy way "to incorporate in historicizing fashion that central element for the history of National Socialism and of the "Third Reich" of the annihilatory capacity of the ideology and of the regime, and to comprehend this totalitarian reality in the interrelated context of Russian and German history. During the Historikerstreit, Hildebrand often used the press as way of attacking Jürgen Habermas over what Hildebrand regarded as Habermas’s unfair criticism of Nolte and Hillgruber. In an 1987 article, Hildebrand argued that both Nazi Germany and the Soviet Union were totalitarian, expansionary states that were destined to come into conflict with each other. Hildebrand argued that in response to concentrations of the Red Army near in the border in the spring of 1941, Hitler engaged in a flucht nach vorn ("flight forward"-i.e responding to a danger by charging on rather then retreating). Hildebrand concluded that "Independently, the National Socialist program of conquest met the equally far-reaching war-aims program which Stalin had drawn up in 1940 at the latest. Hildebrand’s critics such as the British historian Richard J. Evans accused Hildebrand of seeking to obscure German responsibility for the attack on the Soviet Union, and of not being well informed on Soviet foreign policy. Some champions of the "preventive war" theory were critical of Hildebrand for using the term Überfall (fell upon) to describe Operation Barbarossa because it implied Hitler still had some freedom of choice in 1941.