'Akilisi Pohiva dismissed Siaosi Sovaleni after parliament was dissolved by the King in August.
No formal reason was given, but there were reports Mr Sovaleni had supported the Speaker of Parliament's decision to ask the King to dissolve parliament.
Mr Sovaleni, who was Climate Change and Environment Minister, is standing in the November elections and says he will continue to push for renewable energy sources in Tonga.
He said action on climate change and strong institutions around good governance were his key platforms.
