It is located on the north shore of Lake Saint-Louis and is bordered on the west by Baie-D'Urfé, on the north by Kirkland and on the east by Pointe-Claire. It was incorporated in 1910 and is named in honour of Benjamin Disraeli, Lord Beaconsfield, Prime Minister of the United Kingdom in the 1860s and 1870s and close confidant of Queen Victoria. It is part of Greater Montreal locally referred to as the West Island.
As part of the 2002–2006 municipal reorganization of Montreal, Beaconsfield was merged into the city of Montreal on January 1, 2002, joining with neighbouring Baie-D'Urfé to create the borough of Beaconsfield–Baie-D'Urfé. After a change of government and a 2004 referendum, both of them voted to demerge and were reconstituted as independent cities on January 1, 2006. However, they remain part of the urban agglomeration of Montreal.
The population of Beaconsfield is mostly English-speaking. Most buildings in Beaconsfield are single-family homes, with some townhouses and Montreal-style apartment buildings. It may be characterized as a bedroom community. Beaconsfield is also home to a recreation centre that contains a pool, an ice rink and a gym.
A wooded area, Angell Woods, occupies much of western Beaconsfield, and is the subject of a campaign to preserve it permanently as a green space.