By the age of 18, Samuel had become an active Liberal. In 1902, he entered parliament and in 1906 held his first junior ministerial office at the Home Office.

In 1909, Samuel became Chancellor of the Duchy of Lancaster with a seat in the Cabinet - the first held by a professing Jew. In 1910, he was appointed Postmaster General and, in 1914, president of the local government board.

During World War I, Samuel began to take part in Zionist activities. He helped Chaim Weizmann* in the work that ultimately led to the Balfour Declaration*.

In 1920, Samuel was appointed the first High Commissioner of Palestine, a position he held until 1925. During his term of office, the Jewish population doubled; extensive Jewish settlement was carried out; local councils were organized and the Hebrew language was recognized as one of the three official languages of the country. However, in general, the yishuv was disappointed by Samuel's efforts to appease Arab extremists.

Samuel returned to politics in England and in 1928 reentered the House of Commons. In 1931 he became Home Secretary in the national government led by Ramsay MacDonald, but in 1932 he resigned as result of policy differences.

Samuel had been knighted in 1920 and in 1937 was made a Viscount. He led the Liberal Party in the House of Lords from 1944 to 1955.

Samuel's interest in the development of the Jewish National Home never dimmed. He was a constant supporter of the Hebrew University and a member of its Board of Governors. He fought against the anti-Zionist policy adopted in the 1939 White Paper*, as well as against Britain's anti-Zionist policy after World War II.