James Ramsay MacDonald (né James McDonald Ramsay; 12 October 1866 – 9 November 1937) was a British statesman and politician who served as Prime Minister of the United Kingdom. The first two of his governments belonged to the Labour Party, where he led a minority Labour government for nine months in 1924 and again between 1929 and 1931. In 1931, MacDonald was expelled from the Labour Party, after he formed a National Government dominated by the Conservative Party and supported by only a few Labour members, his premiership of which lasted until 1935.

MacDonald, along with Keir Hardie and Arthur Henderson, was one of the three principal founders of the Labour Party in 1900. He was chairman of the Labour MPs before 1914 and, after an eclipse in his career caused by his opposition to the First World War, he was Leader of the Labour Party from 1922. The second Labour Government (1929–1931) was dominated by the Great Depression. He formed the National Government to carry out spending cuts to defend the gold standard, but it had to be abandoned after the Invergordon Mutiny, and he called a general election in 1931 seeking a "doctor's mandate" to fix the economy.

The National coalition won an overwhelming landslide and the Labour Party was reduced to a rump of around 50 seats in the House of Commons. His health deteriorated and he stood down as prime minister in 1935, remaining as Lord President of the Council until retiring in 1937. He died later that year.

MacDonald's speeches, pamphlets and books made him an important theoretician. Historian John Shepherd states that "MacDonald's natural gifts of an imposing presence, handsome features and a persuasive oratory delivered with an arresting Highlands accent made him the iconic Labour leader". After 1931, MacDonald was repeatedly and bitterly denounced by the Labour movement as a traitor to its cause. Since the 1960s, some historians have defended his reputation, emphasising his earlier role in building up the Labour Party, dealing with the Great Depression, and as a forerunner of the political realignments of the 1990s and 2000s.

MacDonald was born at Gregory Place, Lossiemouth, Moray, Scotland, the illegitimate son of John MacDonald, a farm labourer, and Anne Ramsay, a housemaid. Registered at birth as James McDonald (sic) Ramsay, he was known as Jaimie MacDonald. Illegitimacy could be a serious handicap in 19th-century Presbyterian Scotland, but in the north and northeast farming communities this was less of a problem; in 1868, a report of the Royal Commission on the Employment of Children, Young Persons and Women in Agriculture noted that the illegitimacy rate was around 15%—nearly every sixth person was born out of wedlock. MacDonald's mother had worked as a domestic servant at Claydale farm, near Alves, where his father was also employed. They were to have been married, but the wedding never took place, either because the couple quarrelled and chose not to marry, or because Anne's mother, Isabella Ramsay, stepped in to prevent her daughter from marrying a man she deemed unsuitable.

Ramsay MacDonald received an elementary education at the Free Church of Scotland school in Lossiemouth from 1872 to 1875, and then at Drainie Parish School. He left school at the end of the summer term in 1881, at the age of 15, and began work on a nearby farm. In December 1881, he was appointed a pupil teacher at Drainie parish school. In 1885, he moved to Bristol to take up a position as an assistant to Mordaunt Crofton, a clergyman who was attempting to establish a Boys' and Young Men's Guild at St Stephen's Church. In Bristol Ramsay MacDonald joined the Democratic Federation, a Radical organisation, which changed its name a few months later to the Social Democratic Federation (SDF). He remained in the group when it left the SDF to become the Bristol Socialist Society. In early 1886 he moved to London.

Following a short period of work addressing envelopes at the National Cyclists' Union in Fleet Street, he found himself unemployed and forced to live on the small amount of money he had saved from his time in Bristol. MacDonald eventually found employment as an invoice clerk in the warehouse of Cooper, Box and Co. During this time he was deepening his socialist credentials, and engaged himself energetically in C. L. Fitzgerald's Socialist Union which, unlike the SDF, aimed to progress socialist ideals through the parliamentary system. MacDonald witnessed the Bloody Sunday of 13 November 1887 in Trafalgar Square, and in response, had a pamphlet published by the Pall Mall Gazette, titled Remember Trafalgar Square: Tory Terrorism in 1887.

MacDonald retained an interest in Scottish politics. Gladstone's first Irish Home Rule Bill inspired the setting-up of a Scottish Home Rule Association in Edinburgh. On 6 March 1888, MacDonald took part in a meeting of London-based Scots, who, upon his motion, formed the London General Committee of the Scottish Home Rule Association. For a while he supported home rule for Scotland, but found little support among London's Scots. However, MacDonald never lost his interest in Scottish politics and home rule, and in Socialism: critical and constructive, published in 1921, he wrote: "The Anglification of Scotland has been proceeding apace to the damage of its education, its music, its literature, its genius, and the generation that is growing up under this influence is uprooted from its past."