Captain Peter Pégus was the original settler of the area now known as Thornlie, which he had called "Coleraine" when granted the land in 1829.

[4] The James family subsequently sold the estate, which had been a productive dairy farm,[5] in 1937 to the mine-manager and investor, Nat Harper.

[7] 92 hectares (228 acres) of Lot 1 were purchased by D. and M. O'Sullivan, and by June 1956 the Gosnells Roads Board had provided approval for the development of the area.

[7] Thornlie was thus established as a residential suburb in the late 1950s as a housing estate aimed mainly at middle-income earners and inner city dwellers.

During this time Thornlie's development was aimed at inner city dwellers who might want to live in a more spacious semi-urban-rural setting.

It is one reason why Thornlie has typically large blocks of 700–900 square metres (7,500–9,700 sq ft) and is often described as one of Perth's leafy suburbs.

The focus of these developments was on providing affordable housing for new home buyers, generally young families.

Some semi-rural land in the western portion, mainly utilised for horse agistment and chicken-farming, was developed in the early 2000s.

Thornlie is primarily a dormitory suburb with strong transport links to employment elsewhere in the metropolitan region.

A range of sporting facilities are available for community use include lawn bowls, tennis courts, a skate park, swimming pool, gyms and ovals for cricket and football.

[8] Thornlie contains Crestwood Estate, a model housing development still noted for its successful implementation of the Radburn design principles.

Crestwood was to be equally efficient and economical as a conventional subdivision, with the same density of homes (1.3 ha or 3.3 acres), but 8% additional open space.

However, the collapse of land values in the early 1970s led to slow takeup of the allotments and significant losses for Sloan.