Battling against the elements, Benedict, 38, wrapped an arm around the ethereal actress as he escorted her down the red carpet in London.
The duo were promoting their new wartime drama, which took home the People’s Choice Award at TIFF this year.
Despite the showers, Benedict and Keira happily signed autographs for the screaming fans who had been waiting – some since as early as 4am – for the star-studded launch.
All eyes were on Keira as she channelled old school Hollywood glamour, dazzling in a floor-length gold gown and adding a pop of colour to her outfit with fuchsia heels.
The 29-year-old actress let her natural beauty shine through as she wore a touch of make-up and parted her brunette waves to the side.
Benedict looked as equally as handsome, cutting a sharp figure in a black suit. The Sherlock star plays the lead Alan Turing – a computer pioneer who helped decipher Nazi German messages and contributed to the end of World War Two.
Benedict admitted that he didn’t know much about his character before he read the script, and speaking to the BBC described Alan as "a true English hero" who "should be on the front cover of text books".
The actor also said that he understood why people drew comparisons between his wartime character and Sherlock. "I didn’t read the script and go 'this is Sherlock in tweed’," he said. " I liked how uncompromising he was and I suppose that’s a strong trait in strong characters."
Keira, who has been good friends with Benedict since the pair starred in Atonement in 2007, plays fellow-code breaker Joan Clarke.
The actress spoke praises of Benedict’s chameleon qualities, saying at the premiere, “You look at him in Atonement and he’s all horrible and a rapist and quite disgusting, and in The Imitation Game he’s a tortured genius who’s affable and misunderstood. He can just do anything really.”