A member of the opposition Tongan Democratic Party, Sangster Saulala, has confirmed he has taken up a ministerial post in the government of Lord Tu'ivakano.
This comes as the Democrats aim to unseat the prime minister next week through a vote of no confidence.
The switch in allegiance of Mr Saulala is expected to tip the numbers in Lord Tu'ivakano's favour.
Radio Tonga reports that Mr Saulala, the People's Representative for Tongatapu 7, has become the Minister of Agriculture, Forestry, Fisheries and Food as of today.
The radio says Mr Saulala attended today's Cabinet meeting.
He reportedly made his decision after a survey of his constituency showed overwhelming opposition to the no confidence motion.
It was revealed earlier this week that Mr Saulala had been made a minister on Sunday two weeks ago but resigned the following day.