SACRAMENTO—California will aim to put five million zero-emission cars on its roads by 2030 under an executive order signed Friday by Democratic Gov. Jerry Brown.

The new policy is a considerable expansion of the state’s efforts to reduce carbon emissions produced by vehicles, and will likely result in millions of new electric vehicles on the roads.

The move comes as Mr. Brown prepares to leave office after eight years, and is pushing to secure his legacy on the environment and burnish his image as a global leader on climate change.

Mr. Brown highlighted the goal during his annual state of the state address on Thursday.

“Zero emission, the sooner the better,” Mr. Brown said during his speech. “To meet our ambitious goals, we will need five million zero-emission vehicles on the road by 2030. Think of all the jobs that will create and how much cleaner our air will be.”