The Rideau Sheep are truly Canadian, bred and developed in Canada. The Rideau Sheep were developed by Agriculture Canada at the Animal Research Centre (ARC) in Ottawa.

The Rideau Breed evolved from a research program that emphasized the development of techniques and procedures for optimal use of selection and crossbreeding to produce strains of sheep which gave a high economic return under intensive and sustained lamb production. Agriculture Canada's research also concentrated on removal of seasonal constraints to breeding, decreasing the lambing interval, increasing litter size and optimizing the efficiency of growth of the market lamb. The Rideau is a distinct genetic strain designed to enhance the maternal characteristics of a flock.

The development of the Rideau started in 1968. Between 1968 and 1974 the Suffolk, Shropshire and Dorset in the original Agriculture Canada flock were combined with the imported breeds East Friesian and the Finnish Landrace. The East Friesian, a large dairy breed with an average of two lambs per lambing was used to enhance the prolificacy and the milking ability of the Rideau. The Finnish Landrace was used to increase prolificacy and decrease the age when the Rideau would reach puberty. In 1974, the Rideau was closed to the introduction of new genetic material. From 1974 to 1977, the numbers within the breed were multiplied with minimal culling to broaden the genetic base. From 1977 to 1986, the Rideau was selected for high fertility and the potential for year-round lambing and to a lesser extent retail cut yield. By 1986, the Rideau was at least 6 to 7 generations from the original synthetic strain when the population was closed in 1974.

In 1988 and 1989, the Rideau breed was released to nucleus flock owners assigned by the Canadian Sheep Breeders' Association. There were 400 Rideau ewes released in flocks across Canada. All ewes and rams released to the industry had been stabilized genetically and were 9 to 12 generations from the original synthetic strain in 1974. Since 1989, the popularity of the Rideau breed has grown rapidly.