Born in Guildford, Surrey and raised in Los Angeles, Collins began performing on screen at the age of two in the BBC sitcom Growing Pains.
In the late 2000s, Collins began acting and modelling more regularly, and she had a career breakthrough with her performance in the sports-drama film The Blind Side, which was the third highest-grossing film of 2009.
Collins played Fantine in the BBC miniseries adaptation of Les Misérables (2018–2019), and, since 2020, she has portrayed Emily Cooper in the Netflix series Emily in Paris.
she received a nomination for the Golden Globe Award for Best Actress – Television Series Musical or Comedy.
In September 2020, she announced her engagement to American film director and writer Charlie McDowell.