The soldier was caught offering to pass military base maps and photographs to an undercover officer posing as an agent for the third country, the court-martial heard.

The man's name, the country he attempted to spy for and the name of the undercover officer who caught him were all suppressed by the court.

He was the first person to be convicted of spying by a New Zealand court and only the second to be tried after a former public servant was acquitted of espionage in 1975.

The soldier admitted to attempted espionage, accessing a computer system for a dishonest purpose, and to knowingly possessing an objectionable publication.

He had copies of a livestreamed video of the March 2019 killing of 51 worshippers at mosques around Christchurch by white supremacist Brenton Tarrant.

The soldier became a person of interest in the aftermath of the Christchurch attack as police cracked down on right-wing extremist groups, the court heard.

While monitoring him, the New Zealand government became aware he had "made contact with a third party, indicating that he was a soldier who was wanting to defect", according to an agreed summary read out by the prosecution.

An undercover officer then made contact with the would-be spy, claiming to be from that foreign nation.

The soldier said he could provide "mapping and photographs, and he could possibly get a covert device into Army Headquarters", the court heard.

He provided telephone directories of several military camps, including information classified as restricted.

The man offered an assessment of vulnerabilities at Linton Military Camp, as well as access codes and information that would allow for unauthorised access to the camp and nearby Ohakea Air Base, the court heard.

During a search of the man's house, service ammunition was found, as was a computer drive containing a video recording of the Christchurch mosque shooting, and the manifesto of the shooter.

The man is yet to be sentenced.