The elderly driver was killed in Cowra as a thunderstorm tore through central New South Wales before settling over Sydney and the coast.
He has not been formally identified, while another four people were injured in Wagga Wagga when high winds ripped off the roofs of their demountable huts.
NSW State Emergency Service crews have received more than 2250 calls and responded to more than 1800 incidents in 24 hours, predominantly for fallen trees and property damage.
More than 120,000 customers have been left without power and 300 electrical hazards are causing concern across the state.
Newcastle is bearing the brunt of the blackouts, with more than 60,000 customers affected, followed by 31,000 in Sydney and 4000 on the Central Coast.
A fallen tree is causing grief at Royal North Shore Hospital, while at Carlingford, in the city's northwest, 14 people required alternative accommodation after losing their roof to the storm.
Severe thunderstorms will combine with a low-pressure weather system, expected to bring up to 80mm of rain until Saturday, the Bureau of Meteorology has warned.
Friday will see the worst of the rain, with up to 100mm predicted in some areas.
A minor flood watch has been issued for the Orara, Coffs Coast, Bellinger and Kalang river catchments, Manning and Gloucester, Myall River, Karuah River, Wollombi Brook and Lower Hunter, and the Paterson and Williams rivers.
