After Richard Burton became a superstar, he insisted on casting his friends from his days at the Old Vic and West End (London's equivalent to New York City's Broadway). Friends of Burton's cast in this movie included Michael Hordern and Robert Hardy. Burton's former leading lady (on-stage and in two movies) Claire Bloom, however, was cast by Martin Ritt. This caused friction for several reasons: Burton had wanted his wife, Dame Elizabeth Taylor, in the role, and he and Bloom had been an item in the 1950s. John le Carré remembers that "off-screen Bloom preserved a dignified distance in her caravan".
Author John le Carré worked for British Intelligence MI5 and MI6 during the 1950s and 1960s and worked in Berlin where this movie is partially set. Le Carré was there when the Berlin Wall was being constructed. Le Carré drew on this real-life experience when he wrote the novel of "The Spy Who Came in from the Cold". The novel is set about a year after the Berlin Wall was built.
In an article for the New Yorker, John le Carré remembered that the presence of Dame Elizabeth Taylor on the set was incredibly disruptive. The Checkpoint Charlie set was re-created at Dublin's Smithfield Market and because these were nighttime shoots, huge crowds would turn out to watch and inevitably delay the filming. The Taylor-Burtons occupied an entire floor of Dublin's Gresham Hotel, and visitors to the set included Franco Zeffirelli and Yul Brynner, whose son, Rock Brynner, was studying in Dublin's Trinity College at the time. On more than one occasion, filming was delayed by the arguing and drunken behavior of Burton and Taylor.
John le Carré said in an interview with The Guardian on April 13, 2013: "I wrote 'The Spy Who Came in from the Cold' at the age of thirty under intense, unshared, personal stress, and in extreme privacy. As an intelligence officer in the guise of a junior diplomat at the British Embassy in Bonn, I was a secret to my colleagues, and much of the time to myself. I had written a couple of earlier novels, necessarily under a pseudonym, and my employing service had approved them before publication. After lengthy soul-searching, they had also approved 'The Spy Who Came in from the Cold'. To this day, I don't know what I would have done if they hadn't."
In a 2016 article for The Guardian, John le Carré revealed fond memories of the shoot: "The director and I got along fine. I enjoyed an amiable relationship with the screenwriter [i.e. Paul Dehn], who as a former instructor in the black arts at a British spy school during World War II, turned out to know much more about espionage than I did. No great liberties were taken with my story, although I no longer see that as a criterion, and my only job was to provide the odd grace note to the screenplay while befriending Richard Burton and keeping a beady eye on his alcohol consumption." Although he recalled "open hostility" between Burton and Martin Ritt, he believed this "fed Burton's sense of alienation, and gave force to his performance."