Gummer made her motion-picture debut as an adult with a minor role in Lasse Hallström's The Hoax (2006), starring Richard Gere. In 2007, she starred with her mother in Michael Cunningham's film adaptation of Susan Minot's novel Evening, playing her mother as a young woman. The film, directed by Lajos Koltai, featured Vanessa Redgrave, Glenn Close, and Claire Danes. She portrayed Sally Adams in the 2008 HBO mini series John Adams, which details the life of the second President of the United States. She made her Broadway debut in the Tony Award–nominated revival of Les liaisons dangereuses in 2008, for which she received critical praise. She also guest-starred on the CBS legal drama The Good Wife in the season 1 episode "Bad" portraying Nancy Crozier. Her character returned again on season 2 episodes "Cleaning House" and "Getting Off".