His mother was born in Zanzibar (part of Tanzania), where her father studied tropical medicine,[2] and later grew up in Kenya and Uganda.

The book investigates various spying techniques, including signals intelligence (Sigint), a form of electronic eavesdropping between countries.

In particular, Hager documented the US-coordinated ECHELON system, through which the five agencies intercept and process huge volumes of international e-mail, fax and telephone communications.

The book describes its tactics of surveillance of meetings, monitoring the press and responding to every letter to the editor, greenwashing, the use of strategic lawsuit against public participation (SLAPPs), cleaning anti-logging graffiti and blotting out campaign posters in public places, and managing to install its pro-logging educational materials into schools.

[citation needed] It was recognised internationally, with investigative journalist Seymour Hersh stating in a review, "Nicky Hager has more knowledge and understanding of the American intelligence world in Afghanistan – both its good and its very bad points – than any reporter I know.

[17] In late November 2022, the New Zealand Security Intelligence Service (NZSIS) apologised to Hager and paid NZ$66,400 in compensation and legal fees after it illegally accessed his phone records in 2012.

The spy agency believed that a member of the Defence Force had illegally provided Hager with information for his book Other People's War.

In August 2019, the acting Inspector-General of Intelligence and Security found that the spy agency had no reasonable grounds for suspecting espionage and had failed to exercise caution when investigating Hager's source.

[20] In mid-June 2018, Hager accepted an apology and compensation for "substantial damages" from the New Zealand Police for raiding his home in 2014 as part of their investigation into the hacking that led to the Dirty Politics book.

[21][22][23] On 21 September 2016, Nicky Hager was subpoenaed by Colin Craig's lawyers to testify as part of the latter's defence in a defamation suit filed by Jordan Williams, the co-founder of the New Zealand Taxpayers' Union.

Hager took the stand as an expert witness and alleged that publications linked to Jordan Williams on Cameron Slater's blog attacked Craig and followed a similar pattern that had been documented in his book.

[24][25] In March 2017, Hager and fellow journalist Jon Stephenson published Hit & Run: The New Zealand SAS in Afghanistan and the meaning of honour.

The book explored the New Zealand Special Air Service's involvement in Operation Burnham, a retaliatory military raid on two Afghan villages, Naik and Khak Khuday Dad, in Afghanistan's Tirgiran Valley in August 2010.

The authors asserted that the NZSAS actions could be considered war crimes and alleged a cover up by the New Zealand Defence Force.

University of Otago law professor Andrew Geddis opined that Operation Burnham damaged the NZDF's trust and credibility.

Left-wing blogger Martyn "Bomber" Bradbury supported Hager and Stephenson's assertions that New Zealand forces had committed war crimes.

[32] The-then Prime Minister Bill English rejected calls for an inquiry into NZSAS actions on the grounds of inaccuracies in Hit & Run.

[39] On 9 April 2018, the Chief Ombudsman Peter Boshier ruled in favour of the New Zealand Defense Force's decision to withhold most of the information relating to Operation Burnham.

[40][41][42] On 11 April, Attorney-General David Parker announced that the Government would be holding an inquiry into Operation Burnham and the allegations in Hit & Run.

[46][47] In the 2023 King's Birthday and Coronation Honours, Hager was appointed an Officer of the New Zealand Order of Merit, for services to investigative journalism.