Russell practiced law in Ireland from 1854 and in England (usually at Liverpool) from 1859. In 1872 he was appointed a queen's counsel. A Liberal Party member of the House of Commons from 1880 to 1894, he served as attorney general under Prime Minister William Ewart Gladstone in 1886 and again in 1892–94. Although he was sympathetic to Irish nationalism, he urged the establishment of an Irish Parliament subordinate to England's, rather than the granting of Home Rule, which would have given the Irish wider power. In 1888–90 he gained fame as principal defense counsel before the Parnell Commission by discrediting much of the testimony against the Irish nationalist leader Charles Stewart Parnell, especially that based on a letter forged by a journalist, Richard Pigott.

Created a lord of appeal in May 1894, Russell then was appointed lord chief justice of England on the death of John Duke, Baron Coleridge (June 14, 1894). His reputation as a great judge was secured by his conduct of the trial of L.S. Jameson and other British subjects who had abortively invaded the Boer state of the Transvaal (December 1895–January 1896). In 1899 he participated in the successful arbitration of the Venezuela–British Guiana boundary dispute that had threatened to lead to war between Great Britain and the United States.