She has self-described herself as “born and raised in London, to a black Guyanese mother and a white English father”. The daughter of Joy Richardson, Richardson-Sellers comes from a family of stage actors. She grew up attending private schools through bursaries and scholarships. In 2013, Richardson-Sellers graduated, with a degree 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, a short-lived ABC drama series that was 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. Her mother, actress Joy Richardson, guest starred as a distant ancestor of Richardson-Sellers’ character on two episodes, “Zari” and “No Country for Old Dads”. After two seasons, she was cast in the new role of shapeshifter Charlie. Richardson-Sellers exited Legends of Tomorrow in 2020 at the end of the series’ fifth season.

In 2017, along with her Arrowverse co-stars, Richardson-Sellers co-founded Shethority (“She + Authority”), an online global collective described as “a positive place for women and the feminine to inspire, empower, and share.” Active members of the initiative include Melissa Benoist, Nicole Maines, Chyler Leigh, Caity Lotz, Tala Ashe, Emily Bett Rickards, Juliana Harkavy, Katie Cassidy, Candice Patton, and Danielle Panabaker. Through social media, women share their own stories and experiences on dealing with self-acceptance, homophobia, sexual harassment at the workplace.

In 2018, Richardson-Sellers appeared in the short film Melody, directed by Bernard Kordieh. In May 2019, it was announced Richardson-Sellers would star in The Kissing Booth 2, directed by Vince Marcello for Netflix.. She plays Chloe in the Kissing Booth 2.