A relation of the Prime Minister Earl Grey, of Reform Bill fame, Grey grew up in the old Whiggish tradition, and was elected to the House of Commons as a Liberal in 1885. He served under Lord Rosebery as Parliamentary Undersecretary for the Foreign Office in Gladstone's last government, from 1892 to 1895. During the Boer War (1899 - 1902), when the Liberals split between radical Pro-Boers and Liberal Imperialists, Grey stood decidedly on the side of the Imperialists like Rosebery and Herbert Henry Asquith.
When the Liberals returned to power in 1905, Grey became Foreign Secretary, a position in which he would serve for eleven years - the longest continuous holder of the office. Despite his lack of knowledge of any foreign languages and general aristocratic distaste for diplomacy, Grey proved a competent Foreign Secretary. Before the outbreak of the First World War, he had many notable accomplishments, including the completion of the Entente with Russia in 1907, the peaceful settlement of the Second Moroccan Crisis, and leading the joint mediation for the end of the Balkan Wars. Although his activist foreign policy, which relied increasingly on the Entente with France and Russia, came under criticism from the radicals within his own party, he maintained his position due to the support of the Conservatives for his "non-partisan" foreign policy.
In 1914, Grey played a key role in the crisis leading to the outbreak of World War I. His attempts to mediate the dispute between Austria-Hungary and Serbia by a "Stop in Belgrade" came to nothing due to the tepid German response, and when Germany declared war on France (3 August) and invaded Belgium (4 August), Grey was able to muster enough support to bring Britain into the war on August 4, 1914, despite initial radical wariness.
In the early years of the war, Grey negotiated several important secret treaties, bringing Italy into the war (1915) and promising Russia the Turkish Straits. He maintained his position as Foreign Secretary when the Conservatives came into the government to form a coalition in May 1915, but when the Asquith government fell due to machinations between Lloyd George and the Tories, Grey went into opposition.
Raised to the Lords as Viscount Grey of Fallodon, Grey continued active in politics, serving as Liberal Leader in the Lords in 1923-1924 despite his increasingly poor eyesight.
He is probably best remembered for a remark he supposedly made to a friend one evening just before the outbreak of the First World War, as he watched lights being extinguished on the street below his office: "The lamps are going out all over Europe; we shall not see them lit again in our lifetime."