They were shielded from deportation under a humanitarian program, Temporary Protected Status.
The President has cancelled TPS programs for various countries in recent months, affecting immigrants from El Salvador, Haiti and Nicaragua.
The extension does not apply to any new or recent applicants from Syria.
For Syrians already living and working in the US, TPS will be extended for another 18 months. But Syrians who entered the country after August 2016 will be excluded from the program.
Created in 1990, TPS allows immigrants from countries deemed unsafe to lawfully live and work in the US.
It is used by hundreds of thousands of people from 10 designated countries that have been hit by problems such as natural disasters or civil conflicts.