She played Lady Sybil Crawley (2010–2012) in the ITV television period drama series Downton Abbey and Emelia Conan Doyle in the 2011 British comedy-drama feature film Albatross.

[4] In 2016 she joined the cast of the biopic feature film England is Mine, about the early life and career of English singer Morrissey, who co-founded the indie rock band The Smiths.

[5] Brown Findlay portrayed Charlotte Wells, a madam's daughter and prostitute, in the three-series run of Harlots (2017–2019), a period drama television series initially screening on ITV Encore in the UK and on Hulu Plus in the US.

"[7] Brown Findlay was cast in the lead role of 17-year-old Emilia Conan Doyle for Albatross, a 2011 British coming-of-age comedy drama film directed by Niall MacCormick, co-starring Julia Ormond, Felicity Jones and Sebastian Koch.

Its premise is a teenage aspiring writer entering the lives of a dysfunctional family on the south coast of England, with bookish young women meeting up with a peer who lacks any boundaries or inhibitions.

[2] She was next cast in two episodes of the British science fiction comedy-drama television show Misfits,[7] where she appeared in the first-season finale as a wholesome religious girl whose superpower is convincing everyone to abandon their delinquent behaviour in favour of celibacy.

[10] Almost immediately after her work in Albatross, Brown Findlay was cast in the ITV period drama television series Downton Abbey as Lady Sybil Crawley, the youngest and most forward-thinking of the Grantham daughters.

[11] During a 2015 interview, Downton Abbey creator Julian Fellowes discussed the plot twist: "Jessica Brown Findlay, who played Sybil, had said she was going to leave right from the beginning.

[13] The episode imagined a dystopian future where people earn merits on exercise bikes and the only way to escape their slave-like existence is to audition for reality TV judges.

In 2016 Brown Findlay joined the cast of a biopic feature film initially entitled Steven, about the early life and career of English singer Morrissey, who co-founded the indie rock band The Smiths.

[22] In 2017 Brown Findlay portrayed Charlotte Wells, a brothel owner's daughter and famed courtesan, in Harlots, a period drama television series created by Alison Newman and Moira Buffini, and inspired by The Covent Garden Ladies by Hallie Rubenhold.