George V's reign began amid the continuing constitutional crisis over the House of Lords, which refused to pass a Parliament Bill limiting its powers (which would remove its power to veto a Bill from the Commons).

After the Liberal government obtained the King's promise to create sufficient peers to overcome Conservative opposition in the Lords (and won a second election in 1910), the Parliament Bill was passed by the Lords in 1911 without a mass creation of peers.

George visited India in 1911, the only monarch to do so as King-Emperor. He was accompanied by his wife, Queen Mary.

In 1914 the First World War broke out. The King made over 450 visits to troops and over 300 visits to hospitals visiting wounded servicemen, he pressed for proper treatment of German prisoners-of-war and he pressed also for more humane treatment of conscientious objectors.

In 1917 anti-German feeling led him to adopt the family name of Windsor (after the Castle of the same name).

Support for home rule for Ireland had grown in the late 19th century. This was resisted by the Unionists in the north and by the Conservative Party. The 1916 Easter Rising in Dublin, and subsequent civil war, resulted in the setting up of the Irish Free State (later to become the Irish Republic) in 1922, while the six northern counties remained part of the United Kingdom. George played a conciliatory role on this, and on other occasions, such as the General Strike of 1926.

George readily accepted the first Labour government in 1924. Following the world slump of 1929, the King persuaded the Labour leader to head a National Government composed of all parties, which won the election of 1931.

The Statute of Westminster of 1931 enacted that Dominion Parliaments could now pass laws without reference to United Kingdom laws, and abolished various reserve powers still possessed by the Crown and Parliament. This paradoxically increased the monarchy's importance, since the Dominions (no longer subordinated to one supreme Parliament at Westminster) were now linked through common allegiance to the Crown.

George started the annual Christmas Broadcast by the sovereign to the Empire (more recently to the Commonwealth), the first being transmitted in 1932.

In 1935, the King celebrated his Silver Jubilee, an occasion of great public rejoicing.

He died in January 1936 and his eldest son Edward succeeded to the throne as Edward VIII.