The Director General of the Security Service is the head of the Security Service (commonly known as MI5), the United Kingdom's internal counter-intelligence and security agency. The Director General is assisted by a Deputy Director General and an Assistant Director General, and reports to the Home Secretary, although the Security Service is not formally part of the Home Office.

Directors General have been:^[1]

1. Maj Gen Sir Vernon Kell, 1909–1940
2. Brigadier 'Jasper' Harker, Acting, June 1940 – April 1941^[2]
3. Sir David Petrie, 1941–1946
4. Sir Percy Sillitoe, 1946–1953
5. Sir Dick White, 1953–1956
6. Sir Roger Hollis, 1956–1965
7. Sir Martin Furnival Jones, 1965–1972
8. Sir Michael Hanley, 1972–1978
9. Sir Howard Smith, 1978–1981
10. Sir John Jones, 1981–1985
11. Sir Antony Duff, 1985–1988
12. Sir Patrick Walker, 1988–1992
13. Dame Stella Rimington, 1992–1996
14. Sir Stephen Lander, 1996–2002
15. Dame Eliza Manningham-Buller, 2002–2007
16. Sir Jonathan Evans, 2007–2013
17. Sir Andrew Parker, 2013–2020
18. Ken McCallum, from 2020

• Chief of the Secret Intelligence Service
• Director of the Government Communications Headquarters