[3][4] Going into private medical practice in County Londonderry, Morrison was also involved in Unionist politics there.
[3] A Presbyterian, he was active in General Assembly meetings, and also took part in medical societies as a reformer.
[4] When Denis Henry, a Catholic, stood for the South Londonderry constituency in the Westminster parliament, Morrison endorsed him.
[6] From 1921, Morrison represented for the as Ulster Unionist Party the Queen's University constituency, in the House of Commons of Northern Ireland and Stormont Parliament, and supported the introduction of the Special Powers Act 1922.
[3][4][7] In the debate on the Criminal Law Amendment Act (Northern Ireland) 1923, he commented on sexual morality in Belfast, as "a very dark picture" below the surface.