From then on it runs parallel to Wallgrove Road north towards the Great Western Highway and the Light Horse interchange, a stack junction with the M4.

In the late 1980s, with the intended construction of a BHP steel mill in Rooty Hill, Blacktown City Council required BHP to construct an arterial route that allowed industrial traffic to bypass the Rooty Hill CBD and the newly opened Davis Overpass.

This led to the planning of the Western Sydney Orbital, which, among its original purposes, was to serve the stillborn second international airport at Badgerys Creek.

In January 2001 the federal government made a commitment to progressively contribute A$356 million to the Western Sydney Orbital project, with the remaining A$1.5 billion required for the design and construction provided by the private sector.

The design, construct, operate and maintain contract worth at least A$2.0 billion was awarded to WSO (Western Sydney Orbital Pty Ltd) by the Roads & Traffic Authority.

In 2020, WSO – then already a business of the NorthWestern Roads Group – submitted an unsolicited proposal to the NSW government to widen the M7 and construct the M7 and M12 Motorway interchange simultaneously.

[14][15] When first incorporated, WSO Co. Pty Limited (commonly known as Westlink) was a consortium owned by Transurban (40%), Macquarie Investment Group (MIG) (40%), Leighton (10%) and Abigroup (10%).

When the M7 opened in December 2005, Transurban and MIG purchased an additional 5% equity interest in Westlink M7 from Leighton and Abigroup.

[18] In August 2008, Transurban and MIG exercised their pre-emptive rights and acquired Leighton's 5% stake equally, increasing their shareholding to 50% each.

[21] Transurban had the pre-emptive right to acquire MIG's share, but declined in January 2009 due to its high price.

[27][28] The Westlink was built as a fully tolled, gateless motorway employing electronic payment, with an initial toll-free period that ended on 15 January 2006.