His practice was chiefly in commercial, railway and patent cases until (June 1885) he was appointed Attorney-General in the Conservative Government in the exceptional circumstances of never having been Solicitor-general, and not at the time occupying a seat in parliament.

As Attorney General Webster was prosecuting in the Eliza Armstrong case, in the autumn of 1885, a major scandal widely reported in the press, involving a child supposedly bought for prostitution for the purpose of exposing the evils of white slavery.

He was elected for Launceston in the following month, and in November exchanged this seat for the Isle of Wight, which he continued to represent until his elevation to the House of Lords.

In 1890 he was leading counsel for The Times in the Parnell inquiry; in 1893 he represented Great Britain in the Bering Sea arbitration; in 1898 he discharged the same function in the matter of the boundary between British Guiana and Venezuela.

[14] The Arthur Webster Hospital, opened in 1905, was presented to the town of Shanklin, Isle of Wight by Lord Alverstone in memory of his son.

He commissioned the architect Edward Blakeway I'Anson to build Winterfold House near Cranleigh in the Surrey Hills in 1886, in a classic late Victorian style, and laid out grounds with flowering trees and shrubs.

Lord Alverstone died at Cranleigh, Surrey, on 15 December 1915,[15] aged 72 and was buried at West Norwood Cemetery under a Celtic cross.