After graduating in 1907, Blomberg entered the General Staff in 1908. Serving with distinction on the Western Front during World War I, Blomberg was awarded the Pour le Mérite. In 1920, Blomberg was appointed Chief of Staff of the Döberitz Brigade, and in 1921 was made Chief of Staff of the Stuttgart Army Area. In 1925, Blomberg was made Chief of Army Training by General Hans von Seeckt. By 1927, Blomberg was a major - general and Chief of the Troop Office. In 1928, Blomberg visited the Soviet Union, where he was much impressed by the high status of the Red Army, and left a convinced believer in the value of dictatorship as the prerequisite for military power. After arguing with the powerful General Kurt von Schleicher in 1929, however, Blomberg was removed from his post and made military commander of East Prussia. During his time as commander of Wehrkreis I, the military district which comprised East Prussia, Blomberg fell under the influence of a Nazi sympathizing Lutheran chaplain, Ludwig Müller, who introduced Blomberg to National Socialism. Blomberg cared little for Nazi doctrines per se, his support for the Nazis being motivated by his belief that only a dictatorship could make Germany a great military power, and that the Nazis were the best party to create a dictatorship for Germany. In 1931, Blomberg visited the U.S., where he openly proclaimed his belief in the certainty and the benefits of a Nazi government for Germany. Blomberg's first wife Charlotte died on 11 May 1932 leaving him with two sons and three daughters. In 1932, Blomberg served as part of the German delegation to the World Disarmament Conference in Geneva, where during his time as the German chief military delegate, he not only continued his pro-Nazi remarks to the press, but used his status of chief military delegate to communicate his views to Paul von Hindenburg, whose position as President made him Supreme Commander in Chief.

In late January 1933, Blomberg was recalled from the World Disarmament Conference to return to Berlin by President von Hindenburg, who did so without informing the Chancellor, General von Schleicher or the Army Commander, General Kurt von Hammerstein. Upon learning of this, Schleicher guessed correctly that the order to recall Blomberg to Berlin meant his government was doomed. When Blomberg arrived at the railroad station in Berlin, he was met at by Major von Kuntzen ordering him to report at once to the Defence Ministry on behalf of General von Hammerstein, and by Major Oskar von Hindenburg ordering him to report at once to the Presidential palace. Over Kuntzen's protests, Blomberg chose to go with Hindenburg to meet his father, who swore him in as Defence Minister.

In 1933, Blomberg rose to national prominence when he was appointed Minister of Defense in Adolf Hitler's government. Blomberg became one of Hitler's most devoted followers, and worked feverishly to expand the size and power of the army. In 1933 Blomberg was made a colonel general for his services. In February 1934, acting on his own initiative, Blomberg had all of the Jews serving in the Reichswehr given an automatic and immediate dishonorable discharge. In this way, 74 Jewish soldiers lost their jobs for no other reason than there were Jewish. The Law for the Restoration of the Professional Civil Service had excluded those Jews who were World War I veterans, so Blomberg's discharge order was his way getting arould the law. In 1935, Blomberg worked hard to ensure that the Wehrmacht complied with Nuremberg Laws by preventing so-called Mischling from serving.

Blomberg had a reputation as something of a lackey to Hitler. As such, he was nicknamed "Rubber Lion" by some of his critics in the army who were less than enthusiastic about Hitler. One of the few notable exceptions was during the run-up to the Night of the Long Knives in 1934. In early June, Reichspräsident Paul von Hindenburg decided that unless Hitler did something to end the growing political tension in Germany, he would declare martial law and turn over control of the government to the army. Blomberg, who had been known to oppose the growing power of the SA, was chosen to inform Hitler of this decision on the president's behalf.

In the same year, after Hindenburg's death, he personally ordered all soldiers in the army to pledge the Reichswehreid (oath of allegiance) not to Volk and Fatherland, but to the new Führer Adolf Hitler, which is thought to have limited later opposition to Hitler.

In 1935, the Ministry of Defense was renamed the Ministry of War; Blomberg also took the title of Commander - in - Chief of the Armed Forces. In 1936, the loyal Blomberg was the first Generalfeldmarschall appointed by Hitler.

Unfortunately for Blomberg, his position as the ranking officer of the Third Reich alienated Hermann Göring and Heinrich Himmler, who conspired to oust him from power. Göring, in particular, had ambitions of becoming Commander - in - Chief himself. On 5 November 1937, the conference between the Reich's top military - foreign policy leadership and Hitler recorded in the so-called Hossbach Memorandum occurred. At the conference, Hitler stated that it was the time for war, or, more accurately, wars, as what Hitler envisioned were a series of localized wars in Central and Eastern Europe in the near future. Hitler argued that because these wars were necessary to provide Germany with Lebensraum, autarky and the arms race with France and Britain made it imperative to act before the Western powers developed an insurmountable lead in the arms race. Of those invited to the conference, objections arose from the Foreign Minister Konstantin von Neurath, Blomberg and the Army Commander in Chief, General Werner von Fritsch that any German aggression in Eastern Europe was bound to trigger a war with France because of the French alliance system in Eastern Europe, the so-called cordon sanitaire, and if a Franco - German war broke out, then Britain was almost certain to intervene rather than risk the prospect of France's defeat. Moreover, it was objected that Hitler's assumption that Britain and France would just ignore the projected wars because they had started their re-armament later than Germany was flawed. Accordingly, Fritsch, Blomberg and Neurath advised Hitler to wait until Germany had more time to re-arm before pursuing a high-risk strategy of localized wars that was likely to trigger a general war before Germany was ready (none of those present at the conference had any moral objections to Hitler's strategy, with which they were in basic agreement; only the question of timing divided them). After the Hossbach Memorandum meeting of November 1937, Blomberg was one of the few who criticised Hitler's plans to go to war no later than 1942, much to Hitler's displeasure.

Göring and Himmler struck in January 1938, when on 12 January Blomberg, then 59, married Erna Gruhn (sometimes referred to as "Eva" or "Margarete"), a 26 year old typist and secretary. A police officer discovered that Gruhn in 1932 had posed for pornographic photos (taken by a Jew with whom she was living at the time) and reported this to the Gestapo and Göring (who had served as best man to Blomberg at the wedding). It has long been claimed that Frau von Blomberg had a criminal record for prostitution, but this is false; Göring chose to misrepresent Frau Blomberg's criminal record as being for prostitution as a way of smearing her husband. Göring then informed Hitler (who had also been a best man at the wedding), and Hitler ordered Blomberg to annul the marriage in order to avoid a scandal and to preserve the integrity of the army. Blomberg refused to annul the marriage, and consequently resigned all of his posts on 27 January 1938 when Göring threatened to make his wife's past public knowledge.

A few days later, Göring and Himmler accused Commander - in - Chief of the Army Werner von Fritsch of being a homosexual. Hitler used these opportunities for major reorganization of the Wehrmacht. Fritsch was later acquitted; together the events became known as the Blomberg - Fritsch Affair.

Blomberg and his wife were subsequently exiled for a year to the isle of Capri. Spending World War II in obscurity, Blomberg was captured by the Allies in 1945, after which time he gave evidence at the Nuremberg Trials. While in detention at Nuremberg, Blomberg died of cancer in 14 March 1946 and was buried without ceremony in an unmarked grave. Later, his remains were cremated and interred in his residence in Bad Wiessee.

His daughter Dorothea got engaged to Leutnant Karl-Heinz Keitel — General Wilhelm Keitel's eldest son — in January 1938, and they got married in May the same year.