The Cabinet Secretary is the most senior civil servant in the United Kingdom and is based in the Cabinet Office. The person in this role acts as the senior policy adviser to the Prime Minister and Cabinet, and as the Secretary to the Cabinet is responsible to all ministers for the efficient running of government. The role is currently occupied by Simon Case.

The Cabinet Office is a ministerial department of the Government of the United Kingdom. It is responsible for supporting the prime minister and Cabinet. It is composed of various units that support Cabinet committees and coordinate the delivery of government objectives via other departments. As of December 2021, it had over 10,200 staff, mostly civil servants, some of whom work in Whitehall. Staff working in the Prime Minister's Office are part of the Cabinet Office.