Lieutenant-Colonel John Keiller MacKay OC DSO VD KC (July 11, 1888 – June 12, 1970) was a Canadian soldier, lawyer and jurist.

[3] As a judge on the High Court, MacKay wrote the judgment in Re Drummond Wren, a landmark 1945 decision overturning an anti-Semitic restrictive covenant in Toronto.

[4] A local labour organization, the Workers' Education Association (WEA), had purchased a property on O'Connor Drive, east of Broadview Avenue in Toronto, for the purpose of building a model "workingman's home",[5] offered as a potential solution to the city's shortage of affordable housing.

After buying the property, the WEA discovered there was a restrictive covenant on the deed preventing the land from being sold to "Jews or persons of objectionable nationality".

The WEA and the Canadian Jewish Congress launched a court action to strike down the restriction and in his decision, issued on October 31, 1945, Mackay declared the covenant illegal and "injurious to the public good".