31 Sussex Avenue was constructed in 1879. 29, 31, 33 Sussex Avenue are heritage listed properties and known as The Three Sisters. 31 Sussex Avenue is the only of these 3 houses - originally designed in the same style - to have retained its distinct turret since construction. 31 Sussex Avenue was heritage listed on 20 June 1973; wheras 29 and 33 Sussex Avenue were listed on 9 November 2016. As of 2020, all 3 of these houses are owned by the University of Toronto. 

31 Sussex Avenue and adjacent properties are part of the Huron-Sussex Area of Special Identity which has special policies in the City of Toronto Official Plan. However, this is distinct and separate from a Heritage Conservation District. 

Around 2013/2014, 31 Sussex Avenue was the subject of a engineering retrofit project known as "Gemini House" which converted this 1870s solid masonry Victorian home into an ecologically and environmentally friendly residence via using modern technologies. This project was via a collaboration between the University of Toronto and Ryerson University. A number of media articles have been published on the subject (see sources section). This also saw the restoration of the exterior of the property and the removal of the white paint.