Anti-whaling activist Peter Bethune will receive support from New Zealand diplomats throughout his trial, which starts in Japan this week.
The 42-year-old was arrested after boarding the Japanese whaling fleet vessel Shonan Maru 2 hoping to make a citizen's arrest of its captain following a collision between it and his anti-whaling boat, Ady Gil, in January.
He was detained on board and then taken to Japan and charged. Prime Minister John Key says Mr Bethune is getting as much support as can be provided.