The decision was adopted unanimously by the 15-nation council on Tuesday.
Drafted by Argentina, the resolution authorised the deployment of up to 7,200 troops and as many as 1,951 international police officers, roughly in line with the recommendations of Kofi Annan, the UN secretary-general.
But while Annan had called for a 12-month extension of the mission's mandate, the United States insisted on just a six-month renewal, council diplomats said.
Without council action, the mandate would have expired at the end of the day.
Annan, who visited Haiti earlier this month, had argued that it would take at least a year to make progress in improving the legal system and local and national governance.
As a compromise, the resolution stated the council's "intention to renew for further periods".
The UN mission was sent into Haiti in June 2004 to support an interim government installed after President Jean-Bertrand Aristide fled into exile under international pressure.