The court said it would hear an appeal by 20 mainly Democratic states of a lower-court ruling that declared part of the statute unconstitutional and cast a cloud over the rest.
Defenders of the Affordable Care Act argued that the issues raised by the case are too important to let the litigation drag on for months or years in lower courts and that the 5th U.S. Circuit Court of Appeals in New Orleans erred when it struck down the health law's now toothless requirement that Americans have health insurance.
The case will be the third major Supreme Court battle over the law popularly known as Obamacare since its passage in 2010. The court has twice upheld the heart of the law, with Chief Justice John Roberts memorably siding with the court's liberals in 2012, amid President Barack Obama's reelection campaign.
The Trump administration supports the total repeal of the law, including its provisions that prohibit insurance companies from discriminating against people with existing health ailments.