Blackman was born in Plaistow, Newham, London. While training to be an actress she actually worked for the Home Office, the British government agency that overseas MI5. Years later, Albert R. Broccoli admitted that Blackman had been cast on the back of her success in the popular British TV spy show The Avengers, despite the fact that the American audience had never even seen the program. Broccoli said, “The Brits would love her because they knew her as Mrs. Gale, the Yanks would like her because she was so good, it was a perfect combination”. Blackman was the first and one of two “Bond girls” older than the actor playing James Bond, and at 39 she was the oldest actress ever to play a Bondgirl.
In a 1965 episode of The Avengers, titled “Too Many Christmas Trees”, John Steed received his Christmas cards, one of which was from Cathy. “A card from Mrs Gale!”, Steed exclaims in delight. Then, reading the inscription, he says in a puzzled voice, “Whatever can she be doing at Fort Knox…?”. It was an inside joke, as Blackman was filming Goldfinger at the time.