David Petrie was born in 1879. After being educated at Aberdeen University Petrie served in the Indian Police from 1900-36. Posts he held included Assistant Director of Criminal Intelligence and Director of the Intelligence Bureau.
In May 1940 Winston Churchill became prime minister. Six months later he sacked Vernon Kell, Director-General of MI5, and replaced him with David Petrie. Over the next four years Petrie brought in experts to form sections for dealing with different types of agent. He also established closer links with MI6 , the Secret Service with responsibility for counter-espionage outside Britain.
One agent claimed that he doubted if Petrie had "more than a B+ mind but he used it, made few, if any, mistakes, and combined courtesy with firmness." Another MI5 officer claimed that Petrie was "one of the best man managers I ever met." Petrie retired in 1946 and was replaced by an outsider, Sir Percy Sillitoe, the former chief constable of Sheffield and Glasgow.
Sir David Petrie died in 1961.
He was a rock of integrity, the type of Scot whose reliability in all conditions was beyond question, with strong and independent judgment, but ready and willing to delegate and to trust.