John Holland chief executive Joe Barr has let slip that the $12.6 billion tunnel will begin operating next September.
"It certainly is on track," Mr Barr told the Victorian Chamber of Commerce and Industry's Future Victoria lunch on Tuesday.
"The trains have been tested at full speed and we're certainly looking forward to day one of operations in September next year."
John Holland is among the consortium building the project, with construction on the twin 9km train tunnels and five underground stations beginning in 2018.
The state budget in May reaffirmed the tunnel connecting South Kensington to South Yarra would open in 2025, a year ahead of schedule.
Precincts Minister Colin Brooks told the crowd the tunnel would transform how Melburnians move around the city and reshape the precincts of Arden, Sunshine, Footscray, Parkville and Richmond.
"It will deliver Melbourne's first ever turn up and go network - allowing more trains to run more often, similar to cities like London, Singapore and New York," he said.
Melbourne's population is forecast to reach nine million by the 2050s, roughly the size of London in 2023.
More residents will be forced to live further away from the jobs they want if the Victorian city doesn't reshape itself, Mr Brooks said.
"The most successful cities all have one thing in common: they all invest in transport infrastructure that encourages multiple employment and economic districts," he added.
The bill to Victorian taxpayers for the tunnel has blown out from the initial $11 billion cost, after the state government and consortium each agreed to pay an extra $1.37 billion in 2020 - an even split of an extra $2.74 billion in costs.
Another $281 million in COVID-related payments was tacked on in May, taking the total taxpayer cost to $12.6 billion.
When announcing his retirement last month, former premier Daniel Andrews pronounced riding a test train through the tunnel at top speed as one of the best experiences of his almost nine years in the top job.
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