The third son of the 7th Duke of Marlborough, Lord Randolph married a famous beauty, Jeanette (“Jennie”) Jerome (1854–1921) of Brooklyn, N.Y., U.S., in 1874, the same year in which he entered the House of Commons. Until 1880 he exercised his talent for satirical oratory against the Conservative government of Benjamin Disraeli, Earl of Beaconsfield. During William Ewart Gladstone's Liberal ministry of 1880–85, he joined three other Conservatives—Sir Henry Drummond Wolff, John Eldon Gorst, and Arthur James Balfour—in forming what became known as the Fourth Party, which advocated a set of views announced as “Tory Democracy.”

Having served as unofficial private secretary to his father, lord lieutenant (viceroy) of Ireland from 1876 to 1880, Churchill was especially interested in the Irish problem. Though opposed to national Home Rule for Ireland, he favoured self-government on the local level and blamed shortsighted British officials for the Irish crisis of the 1880s. The majority of the Conservative Party agreed with the Liberal government's coercion policy toward Ireland, but Lord Randolph allowed the Irish nationalists, led by Charles Stewart Parnell, to understand that the Conservatives would oppose coercion in return for Irish votes in the general election of 1885. It was said that the Liberals underwent a forced conversion to Home Rule to counteract that promise.

Throughout this period, Churchill attempted to create a new Conservatism with a truly popular appeal and to secure power for the rank-and-file constituency representatives in the party's central organization. Older Conservative leaders, especially Robert Cecil, 3rd Marquess of Salisbury, rejected his approach, and the party split in 1884 over Churchill's election as chairman of the National Union of Conservative Associations. Lord Salisbury and Churchill both made concessions, however, and the reunited party won the vote of confidence of June 1885, Salisbury becoming prime minister. Appointed secretary of state for India, Churchill, who had attacked British imperialism in Egypt and elsewhere, ordered the Third Anglo-Burmese War (Anglo-Burmese Wars) (November 1885), leading to the annexation of all of Burma (Myanmar). He left office with Salisbury on Feb. 1, 1886, after a rupture between the Conservatives and Irish nationalists led to the Conservatives' loss of most of the votes of the Irish bloc in the House of Commons.

When the Conservatives returned to power on July 25, 1886, Salisbury appointed Churchill to the Exchequer and the Commons leadership. Evidently wishing to be the actual head of the government, Churchill alienated most of his colleagues; unable to effect a reconciliation, Salisbury waited for Churchill to defeat himself. He did so with his first budget, which, because it reduced the service estimates, was unacceptable to W.H. Smith, the secretary of state for war. On Dec. 20, 1886, Churchill sent Salisbury his resignation contingent on the prime minister's choice between the policies of the Exchequer and the War Office. When the prime minister backed Smith, Churchill published his resignation in The Times of London on December 23. He may have expected a popular outcry in his favour, but none was heard; since the budget struggle had been kept secret, the public considered his action pointless.

Although he remained in the House of Commons until his death, Churchill lost interest in politics and devoted much time to horse racing. His last years were tragic, a general syphilitic paresis deranging his mind and killing him slowly and painfully.