[4][2] Her older brother Francis is a director who has worked for fashion designer Michael Kors and singers Pixie Lott and Birdy.

[4] In 2005 she landed a lead role in the Indian film Dil Jo Bhi Kahey...,[8] but it did not fare well at the box office.

In television, her breakthrough was in season three of the Showtime drama series The Tudors (2009) as Jane Seymour,[2] where she replaced actress Anita Briem.

In the following years, she starred in the television film The Lost Future (2010) alongside Sam Claflin; and in the ABC series Pan Am (2011), which was cancelled after one season.

[13] In 2014, she joined The Conjuring Universe with a leading role in the horror film Annabelle, directed by John R. Leonetti and produced by James Wan.

[20] In 2019, Wallis joined Showtime's mini-series The Loudest Voice as Laurie Luhn, Head of Booking at Fox News Channel and Roger Ailes's long-time "mistress".

[26] Its premiere at the South by Southwest festival in March 2020 was cancelled due to the COVID-19 pandemic; it was finally released on DirecTV on 16 July 2020.

Scheduled by Warner Bros to premiere in August 2020, the release was postponed due to the COVID-19 pandemic, opening on 10 September 2021, simultaneously in theaters and on HBO Max.

[31][32][33] The film is a tribute to the giallo genre,[34] and follows Madison Mitchell, played by Wallis, who is "paralyzed by shocking visions of grisly murders," and as her torment continues, "discovers that these waking dreams are in fact terrifying realities.

[36][37] This same year, Wallis appeared in the science fiction action film Boss Level directed by Joe Carnahan, starring Frank Grillo and Mel Gibson[38] and starred in Agata Alexander's science fiction thriller Warning, alongside Alice Eve and Alex Pettyfer.

[39][40] In September 2021, the Christmas comedy Silent Night, directed by Camille Griffin, premiered at the Toronto International Film Festival.

[42] In March 2024, Wallis joined Amazon MGM Studios' sci-fi thriller entitled Mercy, alongside actors Rebecca Ferguson and Chris Pratt.

[49] In April 2020, during the COVID-19 pandemic, Wallis teamed up with her friend and fashion designer Georgia Hardinge to raise funds for the charity Age UK.

The donations made to #SaveWithStories will help children and families most affected by the COVID-19 crisis around the world by providing them with food, access to early learning resources and household goods.