The disputed legislation was due to expire at midnight on December 31.
The Senate reconvened late on Thursday, and in a quick vote approved the one-month extension.
The extension will allow time for lawmakers to consider changes that will protect civil liberties.
It represents a defeat for US President George W Bush and his Republican allies, who had initially lobbied hard for an indefinite extension, but faced an outcry after recent revelations he had authorised eavesdropping on US citizens suspected of links to terrorism without a court order.
The legislation gives the US government sweeping authority for monitoring suspected terrorists, including controversial provisions on accessing library records and roving wiretaps.
Some Republicans crossed the floor to join opposition Democrats in forcing the White House to accept only a temporary renewal.
Mr Bush issued a statement praising lawmakers in the House for voting to extend the legislation and accused his Democratic opponents of jeopardising the country's national security.
"The Senate Democratic Leader boasted last week that the Senate Democrats had 'killed the Patriot Act.' Our nation's security must be above partisan politics," Mr Bush said.
Senate Democratic minority leader Harry Reid has said his fellow party members had blocked a permanent renewal of the law until potential threats to civil liberties could be resolved.
Initially passed after the September 11, 2001 terrorist attacks, the Patriot Act expanded the authority of the federal government to conduct secret searches, obtain private records, intercept telephone calls and take other actions in the effort to track down suspected terrorists.