The child was hit by a Toyota Rav4 on East End Road, East Finchley, on Wednesday evening, Scotland Yard said.
The force said it was called to the scene by the London Ambulance Service (LAS) shortly after 7pm.
A spokesperson said: ‘At the scene a three-year-old boy had been in collision with a Toyota Rav4.
‘The injured child was taken to a north London hospital by LAS where he was sadly pronounced dead shortly after arrival. Next of kin have been informed.’
Police said the driver of the car stopped at the scene and has not been arrested.
An investigation into the tragedy has been opened and officers appealed for anyone with dashcam footage or who witnessed the incident first-hand to come forward.
They were asked to call the Metropolitan Police's Serious Collision Investigation Unit on 020 8246 9820, on 101, or Tweet @MetCC quoting CAD 7373/22 MAY.