The 31-year-old from Scotland was the judge's wildcard and one of five finalists who performed with the BBC National Orchestra of Wales at St David's Hall, Cardiff.
The week-long competition featured 20 young classical singers.
They were selected from an original list of 400 entrants before auditions.
Ms Morison was presented with the Cardiff Trophy and £15,000 prize money.
The other finalists were round winners Kang Wang, 29, a tenor from Australia, Anthony Clark Evans, 32, a baritone from the USA, Ariunbaatar Ganbaatar, 29, a baritone from Mongolia and Louise Alder, 30, a soprano from England.
Ms Alder was awarded the Dame Joan Sutherland Audience Prize.
The Welsh representative in the competition was Sioned Gwen Davies, a mezzo soprano from Colwyn Bay, Conwy county.
The final's judging panel was made up of director of Welsh National Opera David Pountney, mezzo-soprano Grace Bumbry, soprano Sumi Jo, baritone Wolfgang Holzmair and conductor Anu Tali.
Mezzo soprano Catriona Morison has been crowned the winner of this year's BBC Cardiff Singer of the World competition.