Claire Foy was born in Stockport, and grew up in Manchester and Leeds. Foy is the youngest of three children. She later moved with her family to Longwick, Buckinghamshire because of her father's employment with Rank Xerox. Her parents divorced when she was just eight years old. Foy attended Aylesbury High School, a girls grammar school, from the age of twelve. Foy eventually then attended Liverpool John Moores University where she studied in Drama and screen studies. She was also trained in a one year course at the Oxford School of Drama. After graduating in 2007, Foy moved out to Peckham to share a house "with five friends from drama school".
While she was studying at Oxford, she appeared in several plays such as Top Girls, Watership Downs, Easy Virtue, and Touched. After appearing on television, Foy made her professional stage debut in "DNA" and "The Miracle" which were two of the trio acts directed by Paul Miller at the Royal National Threate in London. She starred as the main character in the televsion show Little Dorrit and was nominated for a RTS Award. She then went on to appear on the televsion show Going Postal and the medival adventure film, Season of the Witch. She later starred in the BBC revival of Upstairs and Downstairs portraying Lady Persephone. Foy then acted in the Channel 4 mini-series called The Promise, broadcasted in 2011. In an interview, she described it as being "her most favourite job ever". Foy then played the main role as Helen in the television movie The Night Watch. In February 2013, she was named as Lady Macbeth in the Shakespeare stage production of Macbeth. In the same year, she had also landed the role of Sonya Karp, a Moroi vampire in the film adaption of Vampire Academy: Blood Sisters.