Morris was born into an elite Montreal family in 1893. She studied with William Brymner and Maurice Cullen at the Art Association of Montreal from 1907-1917 participating from 1914-1957 in the annual Spring Exhibition of the AAM.
Her mother's cousin, portrait painter, Robert Harris took an active interest in Kathleen's career and family friend Eric Brown, director of the National Gallery had one of her works purchased for its collection.
In 1920 Morris joined the Beaver Hall Group of Painters and also participated in the exhibitions of The Canadian Group of Painters, becoming a member in 1940. From 1923-1929 she lived in Ottawa and exhibited with the Art Association of Ottawa and the James Wilson and Co. gallery.
In winter Morris would often take sketching trips to Quebec City , the Laurentians or Berthierville, all of which along Montreal and Ottawa, would be the inspiration for the winter horse and sleigh and market scenes for which she is best known.
In 1929 she was elected an Associate member of the Royal Canadian Academy of Arts and from 1916- 1958 particiated in the annual RCA exhibitions.
She passed away in Rawson, Quebec in 1986.