Opposition Leader Bill Shorten will announce $700 million in funding for a train line to Ellenbrook in Perth's northeast if Labor wins the next federal election.
The money will be part of a $1.6 billion fund Mr Shorten committed to WA earlier this year as a "top-up" for the far-lower share of GST it currently receives compared with other states.
The rail project is part of the McGowan government's major $2.5 billion Metronet project, which significantly expands the city's rail network.
The federal government agreed to reallocate money from the now abandoned Perth Freight Link road project to Metronet and other transport projects this year despite previously say it could not be done.
WA Transport Minister Rita Saffioti says the Ellenbrook line will be running by 2022.
WA Opposition Leader Mike Nahan said this week the state government should scrap Metronet because of its budget woes, which included a $400 million shortfall after the Liberals blocked Labor's proposed hike in gold royalties.