Best won the 2005 Olivier Award for Best Actress for playing the title role in "Hedda Gabler". She made her Broadway debut in the 2007 revival of "A Moon for the Misbegotten", winning the Drama Desk Award for Outstanding Actress in a Play, and receiving the first of two nominations for the Tony Award for Best Actress in a Play; the second was for the revival of "The Homecoming" in 2008. She returned to Broadway in the 2015 revival of "Old Times". She was cast as Rhaenys Velaryon in HBO’s House of the Dragon.