He was born at Racconigi, in Piedmont. He was the third child, and the only son, of King Victor Emmanuel III of Italy and Princess Elena of Montenegro. He served as the last King of Italy for slightly over a month, from 9 May 1946 to 12 June 1946. He renounced the title of King of Albania, which was held by his father after Italy's invasion of the country, and personally asked King Zog I for forgiveness for taking his throne. Umberto was married in Rome on 8 January 1930 to Marie José of Belgium (1906 – 2001). His children included: Maria Pia (born 1934), Vittorio Emanuele (born 1937), Maria Gabriella (born 1940) and Maria Beatrice (born 1943).

The Prince of Piedmont was born in Racconigi and educated to a military career and in time became the commander in chief of the Northern Armies, and then of the Southern ones. However his role was merely formal, the concrete command belonging to Benito Mussolini. By mutual agreement Umberto and Mussolini always kept at distance. An attempt on the life of the Prince had taken place in Brussels on 24 October 1929, the day of the announcement of his betrothal to Princess Marie José. The Prince was about to lay a wreath on the Tomb of the Belgian Unknown Soldier at the foot of the Colonne du Congrès. With a cry of 'Down with Mussolini!' the culprit, Fernando de Rosa, fired a single shot that missed the Prince of Piedmont. De Rosa was arrested and under interrogation claimed to be a member of the Second International.

It has been conjectured that Mussolini had collected a secret dossier on Umberto, but this folder (which is said to have been found after the dictator was shot), was never seen.

Following the Savoyards' tradition ("Only one Savoy reigns at a time"), he kept apart from active politics until he was finally named Lieutenant General of the Realm. Only in one case, while he was in Germany for a royal wedding, did he make an exception (Adolf Hitler asked for a meeting). This action was not considered proper, given the international situation, and afterwards Umberto was even more rigorously excluded from political events.

On 29 October 1942, Umberto was awarded the rank of Marshal of Italy (Maresciallo d'Italia).

In 1943, the Crown Princess Maria José, the daughter of King Albert I of Belgium, involved herself in vain attempts to arrange a separate peace treaty between Italy and the United States, and her interlocutor from the Vatican was Monsignor Giovanni Battista Montini, a senior diplomat who later became Pope Paul VI. Her attempts were not sponsored by the king and Umberto was not (directly, at least) involved in them. After her failure (she never met the American agents), she was sent with her children to Sarre, in Aosta Valley, and isolated from the political life of the Royal House.

Following the overthrow of Benito Mussolini in 1943, King Victor Emmanuel handed over his constitutional functions to Umberto, who was made Lieutenant General of the Realm, and left Italy for Egypt. Umberto earned for himself widespread praise for his role in the following three years. Some believe that had Victor Emmanuel III handed over the throne in 1943, the monarchy would have won the 1946 referendum on its survival. Victor Emmanuel's failure to do so proved to be one of his many major misjudgments.

Many Italian monarchists expressed doubts about the correctness of the referendum, claiming that millions of voters, many of them pro-monarchist, were unable to vote because they had not yet been able to return to their own local areas to register. Nor had the issue of Italy's borders, and so the voting rights of those in disputed areas, been satisfactorily clarified. Other allegations too have been made about voter manipulation, while even the issue of how to interpret the votes became controversial, as it appeared that not just a majority of those validly voting but of those votes cast (including spoiled votes), was needed to reach an outcome in the event the monarchy lost by a tight margin.

Umberto had by the time of the referendum become king, Victor Emmanuel having reluctantly and belatedly abdicated a few weeks before. Umberto served as king for 33 days. The monarchy formally ended on 12 June 1946 and Umberto became a king in exile, leaving Italy forever. Prime Minister Alcide de Gasperi assumed office as Italy's interim Head of State.

Umberto and Maria José separated in exile; it was an arranged marriage, following a long tradition of royal families, even if some observers alleged that she was really fascinated by her husband.

Some academics have explored Umberto's possible homosexuality. As early as the 1920s, Mussolini had collected a dossier on his private life for purposes of blackmail. Certainly during the war, newspapers asserted that Umberto was homosexual, and information continued to be spread in the lead-up to the post-war referendum on the monarchy in the hope of influencing the outcome. It is, however, unclear to what extent such rumours could be substantiated. Umberto's custom of giving a fleur-de-lismade of precious stones to favoured young officials in his entourage was well known, and Umberto's lovers may have included Luchino Visconti and Jean Marais; as a former army lieutenant who published details of Umberto's advances to him. Except for public appearances, Umberto and Maria Jose generally lived apart.

King Umberto lived for 37 years in exile, in Cascais in Portugal, a popular old gentleman, nicknamed "Europe's grandfather", at many of Europe's royal weddings. During Umberto's lifetime, the 1947 constitution of the Italian Republic barred all male heirs to the defunct Italian throne from setting foot on Italian soil again. Female members of the Savoy family were not barred except consort queens. President Sandro Pertini wanted Umberto to be allowed to return to his native country by the Italian parliament when he was dying in 1983. Ultimately, however, he died in Geneva. No representative of the Italian government attended his funeral.