Wilhelm was born on 27 January 1859 at the Crown Prince's Palace, Berlin, to Prince Frederick william of Prussia (the Future Frederick III) and his wife, Victoria, Princess Royal, the eldest daughter of Britain's Queen Victoria. At the time of his birth, his great-uncle Frederick william IV was king of Prussia, and his grandfather and namesake Wilhelm was acting as Regent. He was the first grandchild of Queen Victoria and Prince Albert, but more important, the first son of the Crown Prince of Prussia, Wilhelm was from 1861 second in the line of succession to Prussia, and also, after 1871, to the newly created German Empire, which, according to the constitution of the German Empire, was ruled by the Prussian King.

In 1863, Wilhelm was taken to England to be present at the wedding of his Uncle Bertie, (later King Edward VII), and Princess Alexandra of Denmark. william attended the ceremony in a Highland costume, complete with a small toy dirk. During the ceremony the four-year-old became restless. His eighteen-year-old uncle Alfred, Duke of Edinburgh, charged with keeping an eye on him, told him to be quiet, but Wilhelm drew his dirk and threatened Alfred. When Alfred attempted to subdue him by force, Wilhelm bit him on the leg. His grandmother, Queen Victoria, missed seeing the fracas; to her Wilhelm remained "a clever, dear, good little child, the great favourite of my beloved Vicky".

As a teenager he was educated at Kassel at the Friedrichsgymnasium. In January 1877, Wilhelm finished high school and on his eighteenth birthday received as a present from his grandmother, Queen Victoria, the Order of the Garter. After Kassel he spent four terms at the University of Bonn, studying law and politics. He became a member of the exclusive Corps Borussia Bonn. Wilhelm possessed a quick intelligence, but this was often overshadowed by a cantankerous temper.

Early conflicts between Wilhelm II and his chancellor soon poisoned the relationship between the two men. Bismarck believed that Wilhelm was a lightweight who could be dominated, and he showed scant respect for Wilhelm's policies in the late 1880s. The final split between monarch and statesman occurred soon after an attempt by Bismarck to implement a far-reaching anti-Socialist law in early 1890.

Wilhelm and his first wife, Princess Augusta Victoria of Schleswig-Holstein, were married on 27 February 1881. They had seven children:

Beginning in 1884, Bismarck began advocating that Kaiser Wilhelm send his grandson on diplomatic missions, a privilege denied to the Crown Prince. That year, Prince Wilhelm was sent to the court of Tsar Alexander III of Russia in St. Petersburg to attend the coming of age ceremony of the sixteen-year-old Tsarevich Nicholas. Wilhelm's behavior did little to ingratiate himself to the tsar. Two years later, Kaiser Wilhelm I took Prince Wilhelm on a trip to meet with the Austro-Hungarian Emperor, Franz Joseph. In 1886, also, thanks to Herbert von Bismarck, the son of the Chancellor, Prince Wilhelm began to be trained twice a week at the Foreign Ministry. One privilege was denied to Prince Wilhelm: to represent Germany at his maternal grandmother, Queen Victoria's, Golden Jubilee Celebrations in London in 1887.

Wilhelm's biographer Lamar Cecil identified Wilhelm's "curious but well-developed anti-Semitism", noting that in 1888 a friend of Wilhelm "declared that the young Kaiser's dislike of his Hebrew subjects, one rooted in a perception that they possessed an overweening influence in Germany, was so strong that it could not be overcome." Cecil concludes:

In 1889 Wilhelm reorganised top level control of the navy by creating a Naval Cabinet (Marine-Kabinett) equivalent to the German Imperial Military Cabinet which had previously functioned in the same capacity for both the army and navy. The Head of the Naval Cabinet was responsible for promotions, appointments, administration, and issuing orders to naval forces. Captain Gustav von Senden-Bibran was appointed as the first head and remained so until 1906. The existing Imperial admiralty was abolished, and its responsibilities divided between two organisations. A new position was created, equivalent to the supreme commander of the army: the Chief of the High Command of the Admiralty, or Oberkommando der Marine, was responsible for ship deployments, strategy and tactics. Vice-Admiral Max von der Goltz was appointed in 1889 and remained in post until 1895. Construction and maintenance of ships and obtaining supplies was the responsibility of the State Secretary of the Imperial Navy Office (Reichsmarineamt), responsible to the Imperial Chancellor and advising the Reichstag on naval matters. The first appointee was Rear Admiral Karl Eduard Heusner, followed shortly by Rear Admiral Friedrich von Hollmann from 1890 to 1897. Each of these three heads of department reported separately to Wilhelm.

British public opinion had been quite favourable toward the Kaiser in his first twelve years on the throne, but it turned sour in the late 1890s. During the First World War, he became the central target of British anti-German propaganda and the personification of a hated enemy.

In addition to the expansion of the fleet, the Kiel Canal was opened in 1895, enabling faster movements between the North Sea and the Baltic Sea.

German foreign policy under Wilhelm II was faced with a number of significant problems. Perhaps the most apparent was that Wilhelm was an impatient man, subjective in his reactions and affected strongly by sentiment and impulse. He was personally ill-equipped to steer German foreign policy along a rational course. It is now widely recognised that the various spectacular acts which Wilhelm undertook in the international sphere were often partially encouraged by the German foreign policy elite. There were a number of notorious examples, such as the Kruger telegram of 1896 in which Wilhelm congratulated President Paul Kruger of the Transvaal Republic on the suppression of the British Jameson Raid, thus alienating British public opinion.

The fact that the High Command might one day abandon the Kaiser had been foreseen in December 1897, when Wilhelm had visited Otto von Bismarck for the last time. Bismarck had again warned the Kaiser about the increasing influence of militarists, especially of the admirals who were pushing for the construction of a battle fleet. Bismarck's last warning had been:

In his first visit to Istanbul in 1889, Wilhelm secured the sale of German-made rifles to Ottoman Army. Later on, he had his second political visit to the Ottoman Empire as a guest of Sultan Abdülhamid II. The Kaiser started his journey to the Ottoman Eyalets with Istanbul on 16 October 1898, then he went by yacht to Haifa on 25 October. After visiting Jerusalem and Bethlehem, the Kaiser went back to Jaffa to embark to Beirut, where he took the train passing Aley and Zahle to reach Damascus on 7 November. The following day, the Kaiser made a famous speech while being at the Mausoleum of Saladin, in which he said:

The Boxer rebellion, an anti-western uprising in China, was put down in 1900 by an international force of British, French, Russian, Italian, American, Japanese, and German troops. The Germans, however, forfeited any prestige that they might have gained for their participation by arriving only after the British and Japanese forces had taken Peking, the site of the fiercest fighting. Moreover, the poor impression left by the German troops' late arrival was made worse by the Kaiser's ill-conceived farewell address, in which he commanded them, in the spirit of the Huns, to be merciless in battle. Wilhelm delivered this speech in Bremerhaven on 27 July 1900, addressing German troops who were departing to suppress the Boxer rebellion in China. The speech was infused with Wilhelm's fiery and chauvinistic rhetoric and clearly expressed his vision of German imperial power. There were two versions of the speech. The Foreign Office issued an edited version, making sure to omit one particularly incendiary paragraph that they regarded as diplomatically embarrassing. The edited version read like this:

When it became clear that Germany would experience a war on two fronts and that Britain would enter the war if Germany attacked France through neutral Belgium, the panic-stricken Wilhelm attempted to redirect the main attack against Russia. When Helmuth von Moltke (the younger) (who had chosen the old plan from 1905, made by General von Schlieffen for the possibility of German war on two fronts) told him that this was impossible, Wilhelm said: "Your uncle would have given me a different answer!" Wilhelm is also reported to have said, "To think that George and Nicky should have played me false! If my grandmother had been alive, she would never have allowed it." In the original Schlieffen plan, Germany would attack the (supposed) weaker enemy first, meaning France. The plan supposed that it would take a long time before Russia was ready for war. Defeating France had been easy for Prussia in the Franco-Prussian War in 1870. At the 1914 border between France and Germany, an attack at this more southern part of France could be stopped by the French fortress along the border. However, Wilhelm II stopped any invasion of the Netherlands.

Wilhelm's most damaging personal blunder cost him much of his prestige and power and had a far greater impact in Germany than overseas. The Daily Telegraph Affair of 1908 involved the publication in Germany of an interview with a British daily newspaper that included wild statements and diplomatically damaging remarks. Wilhelm had seen the interview as an opportunity to promote his views and ideas on Anglo-German friendship, but due to his emotional outbursts during the course of the interview, he ended up further alienating not only the British, but also the French, Russians, and Japanese. He implied, among other things, that the Germans cared nothing for the British; that the French and Russians had attempted to incite Germany to intervene in the Second Boer War; and that the German naval buildup was targeted against the Japanese, not Britain. One memorable quotation from the interview was, "You English are mad, mad, mad as March hares." The effect in Germany was quite significant, with serious calls for his abdication. Wilhelm kept a very low profile for many months after the Daily Telegraph fiasco, but later exacted his revenge by forcing the resignation of the chancellor, Prince Bülow, who had abandoned the Emperor to public scorn by not having the transcript edited before its German publication. The Daily Telegraph crisis deeply wounded Wilhelm's previously unimpaired self-confidence, and he soon suffered a severe bout of depression from which he never fully recovered. He lost much of the influence he had previously exercised in domestic and foreign policy.

On 8 June 1913, a year before the Great War began, The New York Times published a special supplement devoted to the 25th anniversary of the Kaiser's accession. The banner headline read: "Kaiser, 25 Years a Ruler, Hailed as Chief Peacemaker". The accompanying story called him "the greatest factor for peace that our time can show", and credited Wilhelm with frequently rescuing Europe from the brink of war. Until the late 1950s, the Kaiser was depicted by most historians as a man of considerable influence. Partly that was a deception by German officials. For Example, President Theodore Roosevelt believed the Kaiser was in control of German foreign policy because Hermann Speck von Sternburg, the German ambassador in Washington and a personal friend of Roosevelt, presented to the President messages from Chancellor von Bülow as messages from the Kaiser. Later historians downplayed his role, arguing that senior officials learned to work around him. More recently Historian John C. G. Röhl has portrayed Wilhelm as the key figure in understanding the recklessness and downfall of Imperial Germany. Thus, the argument is made that the Kaiser played a major role in promoting the policies of naval and colonial expansion that caused the sharp deterioration in Germany's relations with Britain before 1914.

Wilhelm was a friend of Archduke Franz Ferdinand of Austria, and he was deeply shocked by his assassination on 28 June 1914. Wilhelm offered to support Austria-Hungary in crushing the Black Hand, the secret organization that had plotted the killing, and even sanctioned the use of force by Austria against the perceived source of the movement—Serbia (this is often called "the blank cheque"). He wanted to remain in Berlin until the crisis was resolved, but his courtiers persuaded him instead to go on his annual cruise of the North Sea on 6 July 1914. Wilhelm made erratic attempts to stay on top of the crisis via telegram, and when the Austro-Hungarian ultimatum was delivered to Serbia, he hurried back to Berlin. He reached Berlin on 28 July, read a copy of the Serbian reply, and wrote on it:

Wilhelm's role in wartime was one of ever-decreasing power as he increasingly handled awards ceremonies and honorific duties. The high command continued with its strategy even when it was clear that the Schlieffen plan had failed. By 1916 the Empire had effectively become a military dictatorship under the control of Field Marshal Paul von Hindenburg and General Erich Ludendorff. Increasingly cut off from reality and the political decision-making process, Wilhelm vacillated between defeatism and dreams of victory, depending upon the fortunes of his armies. Nevertheless, Wilhelm still retained the ultimate authority in matters of political appointment, and it was only after his consent had been gained that major changes to the high command could be effected. Wilhelm was in favour of the dismissal of Helmuth von Moltke the Younger in September 1914 and his replacement by Erich von Falkenhayn. In 1917, Hindenburg and Ludendorff decided that Bethman-Hollweg was no longer acceptable to them as Chancellor and called upon the Kaiser to appoint somebody else. When asked whom they would accept, Ludendorff recommended Georg Michaelis, a nonentity whom he barely knew. The Kaiser did not know Michaelis, but accepted the suggestion. Upon hearing in July 1917 that his cousin George V had changed the name of the British royal house to Windsor, Wilhelm remarked that he planned to see Shakespeare's play The Merry Wives of Saxe-Coburg-Gotha. The Kaiser's support collapsed completely in October–November 1918 in the army, in the civilian government, and in German public opinion, as President Woodrow Wilson made clear that the Kaiser could no longer be a party to peace negotiations. That year also saw Wilhelm sickened during the worldwide 1918 flu pandemic, though he survived.

His third visit was on October 15, 1917, as the guest of Sultan Mehmed V.

Wilhelm's hopes of retaining at least one of his crowns was revealed as unrealistic when, in the hope of preserving the monarchy in the face of growing revolutionary unrest, Chancellor Prince Max of Baden announced Wilhelm's abdication of both titles on 9 November 1918. Prince Max himself was forced to resign later the same day, when it became clear that only Friedrich Ebert, leader of the SPD, could effectively exert control. Later that day, one of Ebert's Secretaries of state (ministers), Social Democrat Philipp Scheidemann, proclaimed Germany a republic.

On 10 November, Wilhelm crossed the border by train and went into exile in the Netherlands, which had remained neutral throughout the war. Upon the conclusion of the Treaty of Versailles in early 1919, Article 227 expressly provided for the prosecution of Wilhelm "for a supreme offence against international morality and the sanctity of treaties", but the Dutch government refused to extradite him, despite appeals from the Allies. King George V wrote that he looked on his cousin as "the greatest Criminal in history", but opposed Prime Minister David Lloyd George's proposal to "hang the Kaiser". President Woodrow Wilson of the United States opposed extradition, arguing that prosecuting Wilhelm would destabilize international order and lose the peace.

Wilhelm first settled in Amerongen, where on 28 November he issued a belated statement of abdication from both the Prussian and imperial thrones, thus formally ending the Hohenzollerns' 400-year rule over Prussia. Accepting the reality that he had lost both of his crowns for good, he gave up his rights to "the throne of Prussia and to the German Imperial throne connected therewith." He also released his Soldiers and officials in both Prussia and the empire from their oath of loyalty to him. He purchased a country house in the municipality of Doorn, known as Huis Doorn and moved in on 15 May 1920. This was to be his home for the remainder of his life. The Weimar Republic allowed Wilhelm to remove twenty-three railway wagons of furniture, twenty-seven containing packages of all sorts, one bearing a car and another a boat, from the New Palace at Potsdam.

Empress Augusta, known affectionately as "Dona", was a constant companion to Wilhelm, and her death on 11 April 1921 was a devastating blow. It also came less than a year after their son Joachim committed suicide.

The following January, Wilhelm received a birthday greeting from a son of the late Prince Johann George Ludwig Ferdinand August Wilhelm of Schönaich-Carolath. The 63-year-old Wilhelm invited the boy and his mother, Princess Hermine Reuss of Greiz, to Doorn. Wilhelm found Hermine very attractive, and greatly enjoyed her company. The couple were wed on 9 November 1922, despite the objections of Wilhelm's monarchist supporters and his children. Hermine's daughter, Princess Henriette, married the late Prince Joachim's son, Karl Franz Josef, in 1940, but divorced in 1946. Hermine remained a constant companion to the aging Emperor until his death.

In the early 1930s, Wilhelm apparently hoped that the successes of the German Nazi Party would stimulate interest in a restoration of the monarchy, with his eldest grandson as the fourth Kaiser. His second wife, Hermine, actively petitioned the Nazi government on her husband's behalf. However, Adolf Hitler, himself a veteran of the First World War, like other leading Nazis, felt nothing but scorn for the man they blamed for Germany's greatest defeat, and the petitions were ignored. Though he played host to Hermann Göring at Doorn on at least one occasion, Wilhelm grew to distrust Hitler. Hearing of the murder of the wife of former Chancellor Schleicher, he said "We have ceased to live under the rule of law and everyone must be prepared for the possibility that the Nazis will push their way in and put them up against the wall!" Wilhelm was also appalled at the Kristallnacht of 9–10 November 1938, saying "I have just made my views clear to Auwi [Wilhelm's fourth son] in the presence of his brothers. He had the nerve to say that he agreed with the Jewish pogroms and understood why they had come about. When I told him that any decent man would describe these actions as gangsterisms, he appeared totally indifferent. He is completely lost to our family". He also stated, "For the first time, I am ashamed to be a German."

In the wake of the German victory over Poland in September 1939, Wilhelm's adjutant, General von Dommes, wrote on his behalf to Hitler, stating that the House of Hohenzollern "remained loyal" and noted that nine Prussian Princes (one son and eight grandchildren) were stationed at the front, concluding "because of the special circumstances that require residence in a neutral foreign country, His Majesty must personally decline to make the aforementioned comment. The Emperor has therefore charged me with making a communication." Wilhelm greatly admired the success which Hitler was able to achieve in the opening months of the Second World War, and personally sent a congratulatory telegram when the Netherlands surrendered in May 1940: "My Fuhrer, I congratulate you and hope that under your marvellous leadership the German monarchy will be restored completely." Hitler was reportedly exasperated and bemused, and remarked to Linge, his valet, "What an idiot!". In another telegram to Hitler upon the fall of Paris a month later, Wilhelm stated "Congratulations, you have won using my troops." In a letter to his daughter Victoria Louise, Duchess of Brunswick, he wrote triumphantly, "Thus is the pernicious Entente Cordiale of Uncle Edward VII brought to nought." Nevertheless, after the Nazi conquest of the Netherlands in 1940, the aging Wilhelm retired completely from public life. In May 1940, when Hitler invaded the Netherlands, Wilhelm declined an offer from Churchill of asylum in Britain, preferring to die at Huis Doorn.

During his last year at Doorn, Wilhelm believed that Germany was the land of monarchy and therefore of Christ, and that England was the land of liberalism and therefore of Satan and the Anti-Christ. He argued that the English ruling classes were "Freemasons thoroughly infected by Juda". Wilhelm asserted that the "British people must be liberated from Antichrist Juda. We must drive Juda out of England just as he has been chased out of the Continent." He believed the Freemasons and Jews had caused the two world wars, aiming at a world Jewish empire with British and American gold, but that "Juda's plan has been smashed to pieces and they themselves swept out of the European Continent!" Continental Europe was now, Wilhelm wrote, "consolidating and closing itself off from British influences after the elimination of the British and the Jews!" The end result would be a "U.S. of Europe!" In a letter of 1940 to his sister Princess Margaret, Wilhelm wrote: "The hand of God is creating a new world & working miracles... We are becoming the U.S. of Europe under German leadership, a united European Continent." He added: "The Jews [are] being thrust out of their nefarious positions in all countries, whom they have driven to hostility for centuries." Also in 1940 came what would have been his mother's 100th birthday, on which he wrote ironically to a friend "Today the 100th birthday of my mother! No notice is taken of it at home! No 'Memorial Service' or... committee to remember her marvellous work for the... welfare of our German people... Nobody of the new generation knows anything about her." This sympathy for his mother is in sharp contrast to the intense animosity he expressed for her during most of her life.

Wilhelm died of a pulmonary embolus in Doorn, Netherlands, on 4 June 1941, aged 82, just weeks before the Axis invasion of the Soviet Union. German Soldiers had been guarding his house. Hitler, however, was reported to be angry that the former monarch had an honor guard of German troops and nearly fired the general who ordered them when he found out. Despite his personal animosity toward Wilhelm, Hitler wanted to bring his body back to Berlin for a state funeral, as Wilhelm was a symbol of Germany and Germans during the previous World War. Hitler felt that such a funeral would demonstrate to the Germans the direct descent of the Third Reich from the old German Empire. However, Wilhelm's wishes never to return to Germany until the restoration of the monarchy were respected, and the Nazi occupation authorities granted him a small military funeral, with a few hundred people present. The mourners included August von Mackensen, fully dressed in his old imperial Life Hussars uniform, Admiral Wilhelm Canaris, and Reichskommissar for the Netherlands Arthur Seyss-Inquart, along with a few other military advisers. However, Wilhelm's request that the swastika and other Nazi regalia be not displayed at his funeral was ignored, and they are featured in the photographs of the event taken by a Dutch Photographer.

Three trends have characterized the writing about Wilhelm. First, the court-inspired Writers considered him a martyr and a hero, often uncritically accepting the justifications provided in the Kaiser's own memoirs. Second, there came those who judged Wilhelm to be completely unable to handle the great responsibilities of his position, a ruler too reckless to deal with power. Third, after 1950, later scholars have sought to transcend the passions of the early 20th century and attempted an objective portrayal of Wilhelm and his rule.

Langer et al. (1968) emphasize the negative international consequences of Wilhelm's erratic personality:

Regarding his attitude towards other religions, Wilhelm II was on friendly terms with the Muslim world. He described himself as the "friend" of the "300 million Mohammedans". Following his trip to Constantinople (which he visited three times — an unbeaten record for any European monarch) in 1898, Wilhelm II wrote to Tsar Nicholas II, “If I had come there without any religion at all, I certainly would have turned Mahommetan!”