Work was originally scheduled to start in March but was delayed due to the Covid-19 lockdown.
It then had to be rescheduled until October 12 to manage lizard relocation that must be carried out in a dry season.
Council transport infrastructure portfolio leader councillor Jenny Condie said the first job for the construction team was to remove lizards along the banks of Ngaio Gorge and rehome them in nearby Trelissick Park.
"We've been waiting for lizards to come out of hibernation, now that they are awake we can start moving them out of harm's way before we start on this critical project, Condie said.
"Working with the Department of Conservation, we've implemented a Lizard Management Plan that will involve checking all the vegetation on the work site for lizards. Each lizard will be captured individually in a breathable cloth bag and transferred across the road to their new home in Trelissick Park.
It's expected the inspection and any lizard relocation will take three to four days to complete.
The two-lane road will revert to one lane at the slip site, which will be controlled by traffic signals.
Wellington Mayor Andy Foster said the work would take up to two years.
"I know this work, will at times, be inconvenient for drivers, cyclists and pedestrians, who need to travel on Ngaio Gorge Rd. But I ask people to be patient, and if possible to use Ngauranga Gorge or Onslow Rd or public transport to help ease congestion, while we deliver this long-term solution for this vital arterial road.
"Construction will initially involve building three retaining walls to widen and realign the road, this is expected to take about a year to complete.
"Once that is finished, stabilisation (securing the area's rock bluffs) of the lower and upper slip sites will be completed and the concrete barriers and shipping containers will be removed."
Ngaio Gorge is considered a primary access road to Wellington City as well as being a critical route if Ngauranga Gorge ever becomes blocked to traffic.
Construction crews will work in Ngaio Gorge between 7am and 6pm, Monday to Saturday, from Monday 12 October until October 2022.
