Coming from a family of stage actors, Richardson-Sellers started acting from a young age. In 2013, Richardson-Sellers graduated, with degrees in Archaeology and Anthropology, from University of Oxford, where she participated in and directed several plays, including Mephisto, Chatroom, and There Will Be Red.

After wrapping filming for her The Force Awakens role, Richardson-Sellers booked her second role as Rebekah Mikaelson in the CW series The Originals in 2014, where the character of Rebekah inhabits a different body after a spell gone wrong. Executive Producer Michael Narducci described her performance as having "an incredibly strong sparkle” and “there’s a great beauty – not only with physical beauty but there’s a great inner beauty – that comes up in her performance. There’s also just this incredible strength."

In early March 2015, it was announced that Richardson-Sellers would play a starring role in Of Kings and Prophets, an ABC drama series that would be filmed in South Africa. In June 2016, it was reported that Richardson-Sellers would be playing Amaya Jiwe/Vixen on the second season of the CW series Legends of Tomorrow, who is the grandmother of the titular character in the CW Seed animated series Vixen.