Erich's mother, Klara Jeanette Henriette von Tempelhoff (1840–1914), was the daughter of the noble but impoverished Friedrich August Napoleon von Tempelhoff (1804–1868) and his wife Jeannette Wilhelmine von Dziembowska (1816–1854), who came from a Germanized Polish landed family on the side of her father Stephan von Dziembowski (1779–1859). Through Dziembowski's wife Johanna Wilhelmine von Unruh (1793–1862), Erich was a remote descendant of the Counts of Dönhoff, the Dukes of Duchy of Liegnitz and Duchy of Brieg and the Marquesses and Electors of Brandenburg.

Ludendorff was born on 9 April 1865 in Kruszewnia near Posen, Province of Posen, Kingdom of Prussia (now Poznań County, Poland), the third of six children of August Wilhelm Ludendorff (1833–1905). His father was descended from Pomeranian merchants who had achieved the prestigious status of Junker.

At age 45 "the 'old sinner', as he liked to hear himself called" married the daughter of a wealthy factory owner, Margarethe Schmidt (1875–1936). They met in a rainstorm when he offered his umbrella. She divorced to marry him, bringing three stepsons and a stepdaughter. Their marriage pleased both families and he was devoted to his stepchildren.

Ludendorff divorced and married his second wife Mathilde von Kemnitz (1877–1966) in 1926. They published books and essays to prove that the world’s problems were the result of Christianity, especially the Jesuits and Catholics, but also conspiracies by Jews and the Freemasons. They founded the Bund für Gotteserkenntnis (in German) (Society for the Knowledge of God), a small and rather obscure esoterical society of Theists that survives to this day. He launched several abusive attacks on his former superior Hindenburg for not having acted in a "nationalistic soldier-like fashion".

He had a stable and comfortable childhood, growing up on their small family farm. Erich received his early schooling from his maternal aunt and had a gift for mathematics, as did his younger brother Hans who became a distinguished Astronomer. He passed the entrance exam for the Cadet School at Plön with distinction, he was put in a class two years ahead of his age group, and thereafter he was consistently first in his class. (The famous World War II General Heinz Guderian attended the same Cadet School, which produced many well-trained German officers.) Ludendorff's education continued at the Hauptkadettenschule at Groß-Lichterfelde near Berlin through 1882.

In 1885, Ludendorff was commissioned as a subaltern into the 57th Infantry Regiment, then at Wesel. Over the next eight years, he was promoted to lieutenant and saw further Service in the 2nd Marine Battalion, based at Kiel and Wilhelmshaven, and in the 8th Grenadier Guards at Frankfurt on the Oder. His Service reports reveal the highest praise, with frequent commendations. In 1893, he entered the War Academy, where the commandant, General Meckel, recommended him to the General Staff, to which he was appointed in 1894. He rose rapidly and was a senior staff officer at the headquarters of V Corps from 1902 to 1904.

Next he joined the Great General Staff in Berlin, which was commanded by Alfred von Schlieffen, Ludendorff directed the Second or Mobilization Section from 1904–13. Soon he was joined by Max Bauer, a brilliant artillery officer, who became a close friend. By 1911, Ludendorff was a full colonel. His section was responsible for writing the mass of detailed orders needed to bring the mobilized troops into position to implement the Schlieffen Plan. For this they covertly surveyed frontier fortifications in Russia, France and Belgium. For instance, in 1911 Ludendorff visited the key Belgian fortress city of Liège.

Deputies of the Social Democratic Party of Germany, which became the largest party in the Reichstag after the German federal elections of 1912, seldom gave priority to army expenditures, whether to build up its reserves or to fund advanced weaponry such as Krupp's siege cannons. Instead, they preferred to concentrate military spending on the Imperial German Navy. Ludendorff's calculations showed that to properly implement the Schlieffen Plan the Army lacked six corps.

Members of the General Staff were instructed to keep out of politics and the public eye, but Ludendorff shrugged off such restrictions. With a retired general, August Keim, and the head of the Pan-German League, Heinrich Class, he vigorously lobbied the Reichstag for the additional men. In 1913 funding was approved for four additional corps but Ludendorff was transferred to regimental duties as commander of the 39th (Lower Rhine) Fusiliers, stationed at Düsseldorf. "I attributed the change partly for my having pressed for those three additional army corps."

Then they turned on the second invading army in the Battle of the Masurian Lakes; it fled with heavy losses to escape encirclement. During the rest of 1914, commanding an Army Group, they staved off the projected invasion of German Silesia by dexterously moving their outnumbered forces into Russian Poland, fighting the battle of the Vistula River, which ended with a brilliantly executed withdrawal during which they destroyed the Polish railway lines and bridges needed for an invasion. When the Russians had repaired most of the damage the Germans struck their flank in the battle of Łódź, where they almost surrounded another Russian Army. Masters of surprise and deft maneuver, they argued that if properly reinforced they could trap the entire Russian army in Poland. During the winter of 1914–15 they lobbied passionately for this strategy, but were rebuffed by OHL.

Ludendorff became increasingly cantankerous, slating his staff without cause, publicly accusing the field marshal of talking nonsense, and sometimes bursting into tears. Bauer wanted him replaced, but instead Oberstabarzt Hochheimer was brought to OHL, he had worked closely with Ludendorff in Poland during the winter of 1915–16 on plans to bring in German colonists, before the war he had a practice in nervous diseases. The Doctor "spoke as a friend and he listened as a friend", convincing Ludendorff that he could not work effectively with one hour of sleep a night and that he must relearn how to relax. After a month away from headquarters his patient had recovered from the severest symptoms of battle fatigue.

In contrast to OHL's questionable interventions in politics and diplomacy, their armies continued to excel. The commanders would agree on what was to be done and then Ludendorff and the OHL staff produced the mass of orders specifying exactly what was to be accomplished. On the western front they stopped packing defenders in the front line, which reduced losses to enemy artillery. They issued a directive on elastic defense, in which attackers who penetrated a lightly held front line entered a battle zone in which they were punished by artillery and counterattacks. It remained German Army doctrine through World War II; schools taught the new tactics to all ranks. Its effectiveness is illustrated by comparing the first half of 1916 in which 77 German Soldiers died or went missing for every 100 British to the second half when 55 Germans were lost for every 100 British.

On 20 November 1917 the British achieved a total surprise by attacking at Cambrai. A short, intense bombardment preceded an attack by tanks which led the infantry through the German wire. It was Ludendorff’s 52nd birthday, but he was too upset to attend the celebratory dinner. The British were not organized to exploit their break-through, and German reserves counterattacked, in some places driving the British back beyond their starting lines. The local German commander had not implemented defense in depth.

On 29 September 1918 Ludendorff and Hindenburg told an incredulous Kaiser that they must have an immediate armistice. A new Chancellor, Prince Maximilian of Baden, approached President Woodrow Wilson but his terms were stiff and the Army fought on. The chancellor told the Kaiser that he and his cabinet would resign unless Ludendorff was removed, but that Hindenburg must remain to hold the Army together. The Kaiser called his commanders in, curtly accepting Ludendorff’s resignation and then rejecting Hindenburg’s. Ludendorff would not accompany the field marshal back to headquarters, "I refused to ride with you because you have treated me so shabbily".

Ludendorff returned to Berlin in February 1919. Staying at the Adlon Hotel, he talked with another resident, Sir Neill Malcolm, the head of the British Military Mission. After Ludendorff presented his excuses for the German defeat Malcolm said "you mean that you were stabbed in the back?", ironically coining a key catchphrase for the German right-wing.

On 12 March 1920 5,000 Freikorps troops under the command of Walther von Lüttwitz marched on the Chancellery, forcing the government led by Friedrich Ebert and Gustav Bauer to flee the city. The putschists proclaimed a new government with a right-wing Politician, Wolfgang Kapp as new "chancellor". Ludendorff and Max Bauer were part of the putsch. The Kapp Putsch was soon defeated by a general strike that brought Berlin to a standstill. The Leaders fled, Ludendorff to Bavaria, where a right-wing coup had succeeded. He published two volumes of annotated —and in a few instances pruned — documents and commentaries documenting his war Service. He reconciled with Hindenburg, who began to visit every year.

In May 1923 Ludendorff had an agreeable first meeting with Adolf Hitler, and soon he had regular contacts with National Socialists. On 8 November 1923, the Bavarian Staatskomissar Gustav von Kahr was addressing a jammed meeting in a large beer hall, the Bürgerbräukeller. Hitler, waving a pistol, jumped onto the stage, announcing that the national revolution was underway. The hall was occupied by armed men who covered the audience with a machine gun, the first move in the Beer Hall Putsch. Hitler announced that he would lead the Reich Government and Ludendorff would command the army. He addressed the now enthusiastically supportive audience and then spent the night in the War Ministry, unsuccessfully trying to obtain the army’s backing. The next morning 3,000 armed Nazis formed outside of the Bürgerbräukeller and marched into central Munich, the Leaders just behind the flag bearers. They were blocked by a cordon of police, firing broke out for less than a minute. Most of the Nazi Leaders were hit or dropped to the ground. Ludendorff and his adjutant Major Streck marched to the police line where they pushed aside the rifle barrels. He was respectfully arrested. He was indignant when sent home while the other Leaders remained in custody. Four police officers and 16 Nazis had been killed, including Ludendorff’s servant.

From 1924 to 1928, he represented the German Völkisch Freedom Party in the Reichstag (legislature). Consistently pursuing a purely military line of thought, Ludendorff developed after the war, the theory of "Total War", which he published as Der totale Krieg (The Total War) in 1935. In this work, he argued that the entire physical and moral forces of the nation should be mobilized, because peace was merely an interval between wars. Ludendorff was a recipient of the Grand Cross of the Iron Cross and the Pour le Mérite.

They were tried in early 1924. Ludendorff was acquitted, but Heinz was convicted of chauffeuring him, given a one-year suspended sentence and fined 1,000 marks. Hitler went to prison but was released after nine months. Ludendorff’s 60th birthday was celebrated by massed bands and a large torchlight parade. In 1924, he was elected to the Reichstag as a representative of the NSFB (a coalition of the German Völkisch Freedom Party (DVFP) and members of the Nazi Party), serving until 1928. Gradually he began to part company with Hitler, but nonetheless was persuaded to run for President in March 1925. He received 1.1 per cent of the vote. No one had a majority, so a second round was needed; Hindenburg entered and was narrowly elected. Ludendorff was so humiliated that he broke off their friendship. In 1927 he refused to stand beside the field marshal at the dedication of the Tannenberg memorial. He attacked Hindenburg abusively for not having acted in a "nationalistic soldier-like fashion". The Berlin-based liberal newspaper Vossische Zeitung states in its article "Ludendorff's hate tirades against Hindenburg — Poisonous gas from Hitler's camp" that Ludendorff as of 29 March 1930, was deeply rooted in Hitler’s Nazi ideology.

On 30 January 1933, the occasion of Hitler’s appointment as Chancellor by President Hindenburg, Ludendorff sent the following telegram to Hindenburg:

Erich Ludendorff died of liver cancer in the private clinic Josephinum in Munich, on 20 December 1937 at the age of 72. He was given — against his explicit wishes — a state funeral organized and attended by Hitler, who declined to speak at his eulogy. He was buried in the Neuer Friedhof in Tutzing.

German mobilization earmarked a single army, the Eighth, to defend their eastern frontier. Two Russian armies invaded East Prussia earlier than expected, the Eighth Army commanders panicked and were fired by OHL, Oberste Heeresleitung, German Supreme Headquarters. OHL assigned Ludendorff as the new chief of staff, while the War Cabinet chose a retired general, Paul von Hindenburg, as commander. They first met on their private train heading east. They agreed that they must annihilate the nearest Russian army before they tackled the second. On arrival, they discovered that General Max Hoffmann had already shifted much of the 8th Army by rail to the south to do just that, in an amazing feat of logistical planning. Nine days later the Eighth Army surrounded most of a Russian army at Tannenberg, taking 92,000 prisoners in one of the great victories in German history. Twice during the battle Ludendorff wanted to break off, fearing that the second Russian army was about to strike their rear, but Hindenburg held firm.

Ludendorff was extremely suspicious of the Social Democrats and leftists, whom he blamed for the humiliation of Germany through the Versailles Treaty. Ludendorff claimed that he paid close attention to the Business element (especially the Jews), and saw them turn their backs on the war effort by — as he saw it — letting profit, rather than patriotism, dictate production and financing.

Other historians consider this text to be a forgery. In an attempt to regain Ludendorff’s favor, Hitler arrived unannounced at Ludendorff’s home on his 70th birthday in 1935 to promote him to field marshal. Infuriated, Ludendorff allegedly rebuffed Hitler by telling him: "An officer is named General Field-Marshal on the battlefield! Not at a birthday tea-party in the midst of peace." He wrote two further books on military themes, demonstrating that he still could think coherently about war despite his warped prejudices.