Andrew Parker, who has been with the Security Service since the early 1980s and led its response to the 7 July attacks on London in 2005, will replace Sir Jonathan Evans on 22 April.
He said: “It’s a great honour to be appointed director general of MI5. I’m extremely proud of the extraordinary work the men and women of MI5 do to keep the country safe in challenging circumstances.
“I look forward to leading the service through its next chapter.”