Shields’ first job was in 2008 narrating the short film Las Vegas New Mexico 1875. She portrayed Lisa Rogan a.k.a. Lisa Royal in a 2009 episode of the USA Network drama In Plain Sight, entitled “In My Humboldt Opinion”, and the voice of a girl watching a gun fight in the 7-minute 2008 Western short film Las Vegas New Mexico 1875. In 2011, Shields appeared on CBS in the Hallmark Hall of Fame movie, Beyond the Blackboard, starring Emily VanCamp. In the television movie, Shields portrayed a homeless child named Grace.

Shields co-starred in The Hunger Games, portraying Primrose Everdeen. She reprised her role in the sequels, The Hunger Games: Catching Fire, The Hunger Games: Mockingjay – Part 1, and The Hunger Games: Mockingjay – Part 2. She has said that “just growing up as the character is going to be really fun”. It was announced in 2015 that Shields would star in the films The Wonder (released in 2017 under the title Into the Rainbow), directed by Norman Stone, and A Fall From Grace, directed by Jennifer Lynch.

On February 24, 2015, Shields was announced as one of the celebrities to compete on season 20 of Dancing with the Stars. Her professional partner was Mark Ballas. At age 14, she is the youngest competitor to ever appear on the show (taking the record from Zendaya, who was 16 when she competed on Season 16). In a shocking turn of events, the couple had been eliminated in the seventh week of competition, (finishing in 7th place) despite receiving consistently high scores from the judges throughout the season.