Kaltenbrunner joined the Nazi Party and his NSDAP number was 300,179. In 1932, he joined the SS in Austria. His SS number was 13,039. He was the Gauredner (district speaker) and Rechtsberater (legal consultant) of the SS Division VIII. In January 1934, Kaltenbrunner was briefly jailed by the Engelbert Dollfuss government with other National Socialists at the Kaisersteinbruch concentration camp. In 1934, he was jailed again on suspicion of High Treason in the assassination of Dollfuss. This accusation was dropped, but he was sentenced to six months for conspiracy. In 1934, Kaltenbrunner married Elisabeth Eder (b. 1908) and they had three children. In addition to the children from his marriage, Kaltenbrunner had twins, Ursula and Wolfgang, (b. 1945) with his long time mistress Gisela Gräfin von Westarp (née Wolf). All of his children survived the war.

From mid 1935 Kaltenbrunner was the leader of the Austrian SS. He assisted in the Anschluss and Hitler promoted him to SS Brigadeführer on the day the Anschluss was completed. On 11 September 1938 he was promoted to the rank of SS Gruppenführer. He was also a member of the Reichstag from 1938.

In July 1940, he was commissioned as a Untersturmführer in the Waffen - SS Reserve. Later in April 1941, he was promoted to Major General (Generalleutnant) of the Police. On 30 January 1943 Kaltenbrunner was appointed Chief of the RSHA, composed of the SiPo (Sicherheitspolizei: the combined forces of the Gestapo and Kripo) along with the SD (Sicherheitsdienst: Security Service). He replaced Reinhard Heydrich, who was assassinated in June 1942. Kaltenbrunner held this position until the end of the war. He was promoted to SS Obergruppenführer und General der Polizei on 21 June 1943. He also replaced Heydrich as President of the International Criminal Police Commission (ICPC), the organization today known as Interpol.

Toward the end of the war, Kaltenbrunner's power increased greatly, especially after the attack on Hitler of 20 July 1944, upon which he gained direct access to the Führer. He was also responsible for conducting kangaroo trials and calling for the execution of all the people who were accused of plotting against Hitler. It was often said that even Heinrich Himmler feared him and he managed to be an intimidating figure with his height, facial scars and volatile temper. It was rumored that he was responsible for Adolf Eichmann's failure to attain the rank of SS Colonel. Kaltenbrunner was also long time friends with Otto Skorzeny and recommended him for many secret missions, allowing Skorzeny to become one of Hitler's valued agents. Kaltenbrunner was also responsible for heading Operation Long Jump, the attempt to assassinate Stalin, Churchill, and Roosevelt. Following Himmler's appointment as Minister of the Interior in August 1943, Kaltenbrunner sent him a letter wherein he argued that Himmler's new powers must be used to reverse the party cadre organization's annexation.

In December 1944, Kaltenbrunner was granted the rank of General of the Waffen - SS. Other SS General Officers were granted equivalent Waffen - SS ranks in 1944 as well, so that in the event that they were captured by the Allies, they would have status as military officers instead of police officials. For those who had held police rank prior to 1944, the SS General's title could become rather lengthy. Kaltenbrunner was listed on the SS rolls in 1945 as Obergruppenführer und General der Polizei und Waffen - SS. On 9 December 1944 he was awarded the Knights Cross of the War Merit Cross with Swords. In addition he was awarded the Golden NSDAP party badge and the Blutorden.

On 18 April 1945, Himmler named Kaltenbrunner Commander - in - Chief of those remaining German forces in Southern Europe. Kaltenbrunner reorganized his intelligence agencies as a stay behind underground net. He divided the sub - commands between Otto Skorzeny, head of the sabotage units, and Wilhelm Waneck, who kept in contact not only with Kaltenbrunner and other centers in Germany, but also with stay behind agents in the southern European capitals.

In late April 1945, Kaltenbrunner fled his headquarters from Berlin to Altaussee, where he had often vacationed and had strong ties. While there, he opposed and thwarted the efforts of local governor August Eigruber to destroy the huge and irreplaceable collection of art stolen by the Nazis from museums and private collections across occupied Europe (more than 6,500 paintings plus statuary) which had been intended for Hitler’s planned Führermuseum in Linz.

These were stored in a nearby extensive complex of salt mines. Eigruber was determined to carry out what he was determined was Hitler's true desire – to prevent the collection from falling into the hands of "Bolsheviks and Jews" by destroying it with explosives set off in the mine. Working with Dr. Emmerin Pöchmüller, the mine overseer, Kaltenbrunner countermanded the order and had the explosives removed. Thus he participated in the salvation of such world treasures as Michelangelo’s Madonna of Bruges stolen from the Church of Our Lady in Bruges, and Jan van Eyck’s Ghent Altarpiece stolen from Saint Bavo Cathedral in Ghent; Vermeer’s The Astronomer and The Art of Painting.

On 12 May 1945 he was captured by a U.S. patrol and arrested.

At the Nuremberg Trials, Kaltenbrunner was charged with conspiracy to commit crimes against peace, war crimes and crimes against humanity. The most notable witness in this trial was Rudolf Höss, the camp commander of the Auschwitz concentration camp.

Kaltenbrunner's close control over the RSHA meant that direct knowledge of and responsibility for the following crimes were ascribed to him:

• Mass murders of civilians of occupied countries by Einsatzgruppen
• Screening of prisoner of war camps and executing racial and political undesirables
• The taking of recaptured prisoners of war to concentration camps, where in some cases they were executed
• Establishing concentration camps and committing racial and political undesirables to concentration and annihilation camps for slave labor and mass murder
• Deportation of citizens of occupied countries for forced labor and disciplining of forced labor
• The execution of captured commandos and paratroopers and protection of civilians who lynched Allied fliers
• The taking of civilians of occupied countries to Germany for secret trial and punishment
• Punishment of citizens of occupied territories under special criminal procedure and by summary methods
• The execution and confinement of people in concentration camps for crimes allegedly committed by their relatives
• Seizure and spoliation of public and private property
• Murder of prisoners in SIPO and SD prisons
• Persecution of Jews
• Persecution of the churches
• Torture of gypsies

During the initial stages of the Nuremberg trials, Kaltenbrunner was absent because of two episodes of subarachnoid hemorrhage. His lawyer Kurt Kaufmann requested that Kaltenbrunner be acquitted on grounds of health complications as he was medically unfit for the trial. Kaltenbrunner's state of health improved and the tribunal denied his request for pardon. When Kaltenbrunner was released from a military hospital he pleaded not guilty to the charges of the indictment served on his person. Kaltenbrunner stressed during cross examination that all decrees and legal documents which bore his signature were "rubber - stamped" and filed by his adjutant(s). Kaltenbrunner was incumbent in his defense that Himmler was culpable for the atrocities committed during his tenure as chief of the RSHA. During the trial he stressed that his position existed only in title and was only committed to matters of espionage and intelligence. The IMT (International Military Tribunal) noted that Kaltenbrunner was a keen functionary in matters involving the sphere of the RSHA's intelligence network, but the evidence also showed that Kaltenbrunner was an active authority and participant in many instances of war crimes and crimes against humanity. On September 30, 1946 the IMT found Kaltenbrunner not guilty in matters of conspiracy for aggression concerning the charge of the indictment. However, Kaltenbrunner was found guilty of war crimes and crimes against humanity. On October 1, 1946 the IMT sentenced Ernst Kaltenbrunner to death by hanging.

Kaltenbrunner was executed by hanging at around 1:40 a.m. on 16 October 1946. Kaltenbrunner's last words were:

Rudolf Höss was born in Baden - Baden into a strict Catholic family. He lived with his mother (Lina née Speck) and father (Franz Xaver Höss). Rudolf was the eldest of three children and the only son. He was baptized Rudolf Franz Ferdinand on 11 December 1901. In his early years, according to his autobiography, he was a lonely child with no playmates his own age, until he entered elementary school, and all of his companionship came from adults. His father, a one time army officer who served in German East Africa, ran a tea and coffee business; he raised his son on strict religious principles and with military discipline, having decided that young Rudolf would enter the priesthood. Höss grew up with an almost fanatical belief in the central role of "duty" in a moral life. In his early years there was a constant emphasis on sin and guilt and the need to do penance.

Höss began turning against religion in his early teens, after an episode in which, he said, his own priest broke the Seal of the Confessional by telling his father about an event at school that young Rudolf had described during confession. Soon afterward, Höss's father died, and Höss began moving toward a military life.

When World War I broke out, Höss served briefly in a military hospital and then, at the age of 14, was admitted to his father's and grandfather's old regiment, the German Army's 21st Regiment of Dragoons. He was sent to fight in the Ottoman Empire. While stationed in Turkey he rose to the rank of Feldwebel (Sergeant) and at the age of 17 was the youngest non - commissioned officer in the army. He was awarded the Iron Cross first and second class, among other medals. Höss also briefly served as commander of a cavalry unit.

After Germany's surrender, Höss completed his secondary education, and then joined up with nationalist paramilitary groups that were forming in the post war chaos — first the East Prussian Volunteer Corps and then the Freikorps Rossbach. Höss participated in guerrilla attacks against Polish people during the Silesian Uprisings and against French occupation forces during the Occupation of the Ruhr.

Höss formally renounced his membership in the Catholic Church in 1922 and soon joined the Nazi Party (Party Member #3240) after hearing Hitler speak in Munich. A year later on 31 May 1923, in Mecklenburg, Höss and members of the Freikorps beat suspected Communist Walther Kadow to death on the wishes of the local farm supervisor, Martin Bormann, who later became Hitler's private secretary. Kadow was believed to have tipped off the French occupational authorities that Höss's fellow Nazi, a paramilitary soldier named Albert Leo Schlageter, was carrying out sabotage operations against French supply lines. Schlageter was arrested and executed on 26 May 1923; soon afterwards Höss and several accomplices, including Martin Bormann, took their revenge on Kadow.

In 1923, after one of the killers gave the tale of the murder to a local newspaper, Höss was arrested and tried as the ring leader. Although he later claimed that another man was actually in charge, Höss said he accepted the blame as the group's leader; he was found guilty and sentenced (on 15 or 17 May 1924) to 10 years in Brandenburg Penitentiary for the crime. Bormann received a one year sentence.

Höss was released in July 1928 as part of a general amnesty and joined the völkisch Artamanen - Gesellschaft ("Artaman League") a nationalist back - to - the - land movement that promoted clean living and a farm based lifestyle. On 17 August 1929, he married Hedwig Hensel (3 March 1908 – 1989), whom he met in the Artaman League. They would have five children together — two sons and three daughters, born between 1930 and 1943: Ingebrigitt, Klaus, Hans - Rudolf, Heidetraut and Annegret.

He applied for SS membership on 20 September 1933, and his application was accepted on 1 April 1934. "In June 1934 came Himmler's call to join the ranks of the active SS - Mann." Höss had first met Himmler in 1929. He came to admire Himmler so much that he considered whatever he said to be "gospel" and preferred to hang his picture rather than Hitler's in his office. That same year, Höss moved to the SS - Totenkopfverbände (Death's Head Units) and in December he was assigned to the Dachau concentration camp, where he held the post of Blockführer. Höss's mentor at Dachau was Theodor Eicke. Höss excelled in his duties and was recommended by his superiors for further responsibility and promotion. By the end of his four years at Dachau, he was serving as administrator of the property of prisoners.

In his autobiography, Höss claimed that he disliked the corporal punishment carried out by the guards of the camps on the prisoners (he avoided them as much as he could), but when he saw his first execution it did not affect him as much; he could not explain why that was.

In 1938 he received a promotion to SS - Hauptsturmführer (captain) and was made adjutant to Hermann Baranowski in the Sachsenhausen concentration camp. He joined the Waffen - SS in 1939.

On 1 May 1940, Höss was appointed commandant of a prison camp in western Poland, a territory Germany had annexed outright and incorporated into the province of Upper Silesia. The camp was built around an old Austro - Hungarian (and later Polish) army barracks near the town of Oświęcim; its German name was Auschwitz. Höss would command the camp for three and a half years, during which he expanded the original facility into a sprawling complex, the place now known as the Auschwitz - Birkenau concentration camp. Höss went to Auschwitz determined "to do things differently" and develop a more efficient killing center than those in which he had previously served. Höss lived at Auschwitz in a villa together with his wife and five children.

The earliest inmates at Auschwitz were Polish prisoners, including peasants and intellectuals, as well as Soviet prisoners of war. At its peak size, Auschwitz was actually three separate facilities (Auschwitz I, Auschwitz II/Birkenau, and Auschwitz III/Monowitz) and was constructed on 8,100 ha (20,000 acres) that had been cleared of all inhabitants. Auschwitz I was the administrative center for the complex; Birkenau was the extermination camp, where most of the killing took place.

In June 1941, according to Höss's later trial testimony, he was summoned to Berlin for a meeting with Reichsführer - SS Heinrich Himmler "to receive personal orders". Himmler told Höss that Hitler had given the order for the physical extermination of Europe's Jews. Himmler had selected Auschwitz for this purpose, he said, "on account of its easy access by rail and also because the extensive site offered space for measures ensuring isolation". Himmler told Höss that he would be receiving all operational orders from Adolf Eichmann. Himmler described the project as a "secret Reich matter", meaning that "no one was allowed to speak about these matters with any person and that everyone promised upon his life to keep the utmost secrecy". Höss said he kept that secret until the end of 1942, when he told one person about the camp's purpose: his wife.

After visiting Treblinka extermination camp (which did not become operational until July 1942) to study its methods of human extermination, Höss, beginning on the 3 September 1941, tested and perfected the techniques of mass killing that made Auschwitz the most efficiently murderous instrument of the Final Solution and the most potent symbol of the Holocaust. According to Höss, during standard camp operations, two to three trains carrying 2,000 prisoners each would arrive daily for periods of four to six weeks. The prisoners were unloaded in the Birkenau camp; those fit for labor were marched to barracks in either Birkenau or one of the Auschwitz camps, while those unsuitable for work were driven into the gas chambers. At first, small gassing bunkers were located deep in the woods, to avoid detection. Later, four large gas chambers and crematoria were constructed in Birkenau to make the killing more efficient and to handle the increasing rate of exterminations.

Höss improved on the methods at Treblinka by building his gas chambers 10 times larger, so that they could kill 2,000 people at once rather than 200. He commented,

Höss experimented with various methods of gassing. According to Eichmann's trial testimony in 1961, Höss told him that he used cotton filters soaked in sulfuric acid in early killings. Höss later introduced hydrogen cyanide, produced from the pesticide Zyklon B, into the killing process, after his deputy Karl Fritzsch tested it on a group of Russian prisoners in 1941. With Zyklon B, he said that it took 3 – 15 minutes for the victims to die and that "we knew when the people were dead because they stopped screaming".

Höss explained how 10,000 people were exterminated in one 24 hour period:

Höss later testified that Himmler himself visited the camp in 1942 and "watched in detail one processing from beginning to end". Eichmann, Höss said, visited the camp and observed its operations frequently.

In his affidavit prepared for the Nuremberg trials in 1946, Höss asserted that local residents were well aware of the camp's purpose:

After being replaced as the Auschwitz commander by Arthur Liebehenschel, on 10 November 1943 Höss assumed Liebehenschel's former position as the chairman of Amt D I in Amtsgruppe D of the SS - Wirtschafts-Verwaltungshauptamt (WVHA); he also was appointed deputy of the inspector of the concentrations camps Richard Glücks.

On 8 May 1944, however, Höss returned to Auschwitz to supervise the operation, known as Aktion Höss, by which 430,000 Hungarian Jews were transported to the camp and killed during 56 days  between May and July of that year. Even Höss' expanded facility could not handle the huge number of victims' corpses, and the camp staff had to dispose of thousands of bodies by burning them in open pits.

In the last days of the war, Höss was advised by Himmler to disguise himself among German Navy personnel. He evaded arrest for nearly a year. When he was captured by British troops — some of whom were Jews born in Germany — on 11 March 1946, he was disguised as a farmer and called himself Franz Lang. His wife told the British where he could be found, fearing that her son, Klaus, would be shipped off to the Soviet Union, where he surely would, at minimum, be sent to the gulag and be tortured. After being questioned and allegedly beaten severely by his captors Höss confessed his real identity.

During the Nuremberg Trials, he appeared as a witness in the trials of Ernst Kaltenbrunner, Oswald Pohl, and the IG Farben corporation. There he gave detailed testimony of his crimes:

On 25 May 1946, he was handed over to Polish authorities and the Supreme National Tribunal in Poland tried him for murder. During his trial, when accused of murdering three and a half million people, Höss replied, "No. Only two and one half million — the rest died from disease and starvation." Höss was sentenced to death on 2 April 1947. The sentence was carried out on 16 April immediately adjacent to the crematorium of the former Auschwitz I concentration camp. He was hanged on gallows constructed specifically for that purpose, at the former location of the camp Gestapo. The message on the board reads:

Höss wrote his autobiography while awaiting execution; it was published in 1958 as Kommandant in Auschwitz; autobiographische Aufzeichnungen and later as Death Dealer: the Memoirs of the SS Kommandant at Auschwitz (among other editions).

After discussions with Höss during the Nuremberg trials at which Höss testified, the American military psychologist Gustave Gilbert wrote the following:

Four days before he was executed, Höss sent a message to the state prosecutor, including these comments: