The decree gives Mr Maduro extra powers to deal with Venezuela's economic crisis, including the right to impose tougher security measures.
The opposition-controlled parliament rejected the decree on Tuesday.
But the Supreme Court, which rarely rules against the government, said the decree was justifiable.
The court upheld the decree because of  what it called "the extraordinary social, economic, political, natural and ecological circumstances that are gravely affecting the national economy."
What has gone wrong in Venezuela?
On Friday, President Maduro declared a state of emergency for 60 days, accusing the business elite of boycotting the economy and the United States of plotting a coup against his socialist government.
In measures published in the government gazette on Monday, the armed forces and local committees now have powers to distribute and sell food.
Authorities will also be allowed to cut the working week in the private sector, as they have done in the public sector, to conserve electricity.
The new measures also allow the government to take control of basic goods or services, which analysts say opens the way to the expropriation of companies.
The opposition has rejected the new measures and is pushing for a referendum to removed Mr Maduro from power.
They began the process two weeks ago by handing in a petition signed by 1.85m people.
But Venezuela's Vice-President Aristobulo Isturiz has ruled out the possibility of a recall referendum against Mr Maduro.
Many Venezuelans blame Mr Maduro for the economic crisis the country is experiencing.
Its economy contracted by 5.7% last year and is expected to shrink further this year. Inflation is at 180%, according to official figures, and there are shortages of medicines and basic food items.
The Venezuelan Supreme Court has ruled that a decree issued by President Nicolas Maduro last week declaring a state of emergency is constitutional.