The four people were walking along Sutton Road in Askern, when they were hit by a blue Volvo S60 car, South Yorkshire Police said.
Two women aged 53 and 54 and a 59-year-old man died from their injuries and a 56-year-old man is being treated in hospital for life-threatening injuries.
The driver, a 24-year-old man, was arrested on suspicion of causing death by dangerous driving.
The families of those involved are being supported by specialist officers, police said.
A spokesman added: “Those involved have not been formally identified and officers would like to remind the public to take care when posting on social media.”
Anyone who witnessed the incident is urged to call police on 101.