what official decree established quebec as a british colony?

Answer 1

While the treaty of paris transferred the territory of New France, including Quebec, to British control, the establishment of Quebec as a colony came with the Royal Proclaimation of 1763.

Answer 2

The Treaty of Paris, 1763, ended the conflict that North Americans call the French Indian War. Britain had decisively beaten France, both in North America and in Europe, and in this treaty England chose to take Canada, including Quebec instead of the lush French West Indies sugar islands of Guadalupe and Martinique. From this treaty, England became the strongest and largest European colonial power.