Over the next three years he held positions in the governments of Lyons, Earle Page, Robert Menzies, and Arthur Fadden.

In October 1916, Harrison joined the Australian Imperial Force and served on the Western Front from December 1917 in the 5th Field Artillery Brigade.

[1] Although Harrison had not previously been politically active, in 1931 he established a branch of Joseph Lyons' All for Australia League in the Sydney suburb of Auburn, within Jack Lang's electorate, with police protection.

In the December 1931 general elections he defeated Walter Marks for the House of Representatives seat of Wentworth, although both had been endorsed by the United Australia Party (UAP).

He went into opposition with the defeat of the Fadden government in October 1941 and almost lost his seat to suffragette and Australian Labor Party candidate Jessie Street in December 1943.

On one occasion he wore a uniform in Canberra, causing Eddie Ward to denounce him as a fake soldier and to accuse him of having been a member of the New Guard.

His wife died in 1941 and in October 1944 he married Linda Ruth Yardley, née Fullerton, a widow and a businesswoman.

[1] Harrison was acting prime minister for two weeks in June 1954, when Menzies was in New Zealand and Fadden was recovering from injuries sustained in a car accident.

[2][3] Harrison resigned from parliament in 1956 and became Australian High Commissioner in London, where he was an outspoken advocate[clarification needed] of the "Old Commonwealth".

[citation needed] The Harrisons returned to Australia in September 1964 and moved to the Sydney suburb of Castle Cove.