The vote was triggered after a series of defections from Mr Sogavare's coalition, which has been in power since 2014.
It is not clear what has caused the defections, but some government supporters suggest it's in response to a proposed anti-corruption bill.
The opposition leader, Derek Sikua, is expected to spell out his reasons for the motion in parliament today.
The government and opposition have spent the past week battling to consolidate their numbers ahead of today's vote.
Late last week, Mr Sogavare announced eight new ministers in his effort to shore up support.