Lawmakers in Haiti have yet to pass an emergency electoral law aimed at ending a political stand-off between the government and the opposition.
This can lead to the parliament's dissolution, and President Michel Martelly could rule by decree.
On Sunday, he said he had reached a last-minute deal with the opposition to hold long-delayed elections.
But a key opposition party was not part of the deal. The parliament's mandate expired at midnight (05:00GMT.)
President Martelly announced late on Sunday that he had agreed with some 20 political leaders to hold elections by the end of this year.
But the left-wing Fanmi Lavalas, which has been at the forefront of anti-government protests, was not part of the agreement.
The opposition earlier said Mr Martelly wanted to derail the deal to rule by decree.
The president says the blame for the delayed elections lies with opposition lawmakers who have refused to pass a key electoral law needed for polls to be held.
Mid-term Senate elections had been originally due in May 2012, while the municipal poll is three years behind schedule.
The crisis comes as Haiti commemorated the fifth anniversary of a devastating earthquake which destroyed most of the county's infrastructure and left hundreds of thousands of people living in temporary camps.
The country has been slow to recover with around 80,000 people still living in squalid tent camps and only 67% having access to latrines.
Prime Minister Laurent Lamothe resigned on 14 December amid a series of anti-government protests.
Mr Martelly named former radio journalist Evans Paul as his replacement, but Mr Paul has not yet been confirmed in the post.