The eastern end of Heathcote Road reopened in both directions after repairs to the westbound lane.
However a reduced speed limit of 40km/h is in place.
The westbound lane between between Princes Highway and New Illawarra Road has been closed since early July due to damage caused by record rainfall, with a tidal flow in place for the last week.
Repairs were finally able to start at the end of last week after it was confirmed the ground beneath the road had stabilised and work continued through Friday night before the reopening about midday on Saturday.
Heathcote MP Lee Evans said, "This steep and heavily vegetated site became unstable under the weight of the record rainfall experienced in Sydney earlier this year, so engineers needed to be sure the land had not slipped to allow work to progress safely and successfully.
"To have emergency road repairs and a once-in-a-generation construction project occur at what is essentially the same location is a truly rare situation for Transport for NSW, and I commend their handling of this huge challenge
"I also recognise the patience and understanding of the many locals and motorists who have had to endure the extreme inconvenience caused by this situation, so it gives me great pleasure to provide this good news about the lane reopening."
For the latest information on emergency repairs to Heathcote Road visit https://nswroads.work/heathcoteworks.