He served as an infantry Major in 3rd Auckland (Countess of Ranfurly's Own) and Northland Regiment Royal New Zealand Territorial Army, later specialising in military intelligence.

Mapp held various party spokesperson roles including Defence, Justice, Foreign Affairs, Industrial Relations and "political correctness eradication."

In a September 2003 house sitting, Mapp criticised the incumbent government's lack of support for the US-led invasion of Iraq.

The 2017 book by Nicky Hager and Jon Stephenson, Hit & Run, alleged that New Zealand forces had committed war crimes against civilians in the Naik and Khak Khudday Dad villages.

[1] On 15 December 2011, in recognition of his term as a Member of the Executive Council of New Zealand, Mapp was granted the right to retain the title The Honourable for the rest of his life.