In 2011, Williams made her professional acting debut as Arya Stark, a tomboyish young girl from a noble family, in the HBO fantasy drama television series Game of Thrones. Chosen from a pool of 300 actresses across England, Arya was Williams's first role in any professional capacity. She has received critical acclaim for her performance in the series, especially in the show's second season. HBO submitted her for consideration in the Outstanding Supporting Actress category for the 2012 Primetime Emmy Awards, although she did not receive a nomination. She won the 2012 Portal Award for Best Supporting Actress – Television, and the Portal Award for Best Young Actor. At 15 years of age, Williams was the youngest actress ever to win in the Best Supporting Actress category. In March 2013, she was nominated for a Young Artist Award for Best Performance in a TV Series – Supporting Young Actress for her work on the show and, in November 2013, won the BBC Radio 1 Teen Award for Best British Actor. She has appeared in all eight broadcast seasons, in July 2018, she announced the completion of her role in series. The final episode aired in May 2019.