Trains will run every four minutes will run in peak times on the city section of the metro, called the M1 line.
It extends the existing Metro in the north-west of Sydney, from Chatswood to Sydenham.
There is a total of 15.5km of line some of which goes under the Harbour.
As many as 37,000 commuters are expected to use the trains during morning peak hour on 45 metro trains running 445 services a day.
Passengers will be able to get from Victoria Cross in North Sydney, under the harbour to Barangaroo in three minutes, between Martin Place and Central in four minutes and from Sydenham to Chatswood in 22 minutes.
Six accessible new stations have been built at Crows Nest, Victoria Cross, Barangaroo, Martin Place, Gadigal and Waterloo, along with new platforms at Central and Sydenham.
Plus while the trains will be underground, passengers will be able to use their mobile phones.
Transport bosses boast there will be a "state-of-the-art" control centre, with 100 CCTV cameras at every station and 38 cameras inside each train.
New bike spaces are also on offer.
Final confirmation of the opening date will be given in coming weeks when the operator successfully completes more than 100 remaining trial running exercises, transport bosses say.
"Excitement is mounting for when commuters will be able to step on-board 445 new metro services deep below the city every day," Transport Minister Jo Haylen said.
"Metro will be the fastest way to travel in and around Sydney CBD and north of the city, including across the harbour, when passenger services on the M1 Line start next month."
