The National Security Adviser (NSA) is a senior official in the Cabinet Office, based in Whitehall, who serves as the principal adviser to the Prime Minister of the United Kingdom and Cabinet of the United Kingdom on all national security issues.

The NSA post was created in May 2010 as part of the reforms that also saw the creation of the National Security Council.

[1] There have been six holders of the office to date, two of whom served more than three years in the post.

[2] Until 2024, the NSA acted as Secretary to the National Security Council, which is chaired by the Prime Minister, and head of the National Security Secretariat in the Cabinet Office.

The National Security Adviser is the principal official adviser to the Prime Minister and Cabinet on national security matters.