Dagmara Domińczyk (doh-MEEN-chik, born July 17, 1976) is a Polish-American actress and author. She's best known for her roles as Mercedès Iguanada in The Count of Monte Cristo (2002), Tania Asher in Rock Star (2001), Agnes Gebhard in Kinsey (2004), Marguerite in The Five People You Meet in Heaven (2004), Katrina on WB's The Bedford Diaries, Suzanne in Running with Scissors (2006), Belva in The Immigrant (2013), Elizabeth Taylor in Big Stone Gap (2013), Stacy in Let's Kill Ward's Wife (2014), Karolina Novotney on HBO's Succession, Ellen in The Assistant (2020), Erika Jensen on HBO's We Own This City (2022), and Elle Sellwyn on AppleTV's Hello Tomorrow! (2023).

In 2013, she released her novel The Lullaby of Polish Girls.