Robertson in the Southern Highlands received the biggest falls in the state, receiving 698mm since Wednesday as of 9am Monday - 500mm on the weekend alone.
Castle Cove was the wettest area in Sydney, recording 456mm since Wednesday.
Sydney itself received 391.6mm, its wettest four-day period since 1990.
Byron Bay in the north recorded more than 300mm, while parts of the south coast recorded 150mm to 200mm.
Dam levels across greater Sydney rose by more than 20 percentage points over the past week, sitting at 64.2 per cent on Monday.
Warragamba Dam's level rose 17.7 percentage points to reach 60.7 per cent.
The RFS says the rain helped firefighters extinguish more than 30 fires, some of which had been burning for months. They include the Gospers Mountain megablaze northwest of Sydney, the large Green Wattle Creek fire southwest of Sydney and the Currowan blaze which ravaged the south.
There were 26 fires left burning in NSW on Monday afternoon, all at the lowest alert level.
Some drought-affected communities in the Southern Tablelands, northwest and central west of the state have welcomed rain, but the Bureau of Meteorology says it will take prolonged follow-up falls to break the drought.
The ACT and Southern Tablelands received about 60mm of widespread rain in the 24 hours to Monday morning.
Areas around Tamworth, Moree and Dubbo have had thunderstorms over the past week but rainfall has varied, with some areas getting 50mm-100mm over seven days and others receiving a lot less.
Australian Associated Press