Her film appearances include Cleopatra (1963), Frenzy (1972), The Eagle Has Landed (1976), The Changeling (1980), Return to Oz (1985), Willow (1988), Fatherland (1994) and Monarch (2000).

Marsh reprised the role in the audio plays Home Truths (2008), The Drowned World (2009), The Guardian of the Solar System (2010), The Five Companions (2011), The Anachronauts (2012), The Light At The End (2013), An Ordinary Life (2014) and The Sontarans (2016).

Marsh featured as Bertha Mason Rochester in the George C. Scott-Susannah York version of Jane Eyre, directed by Delbert Mann.

With Eileen Atkins, Marsh created the British period drama Upstairs, Downstairs and played the role of the house parlourmaid Rose Buck for the duration of the series, from 1971 until 1975.

Her television films include Goliath Awaits (1981), See China and Die (1981), Master of the Game (1984), The Corsican Brothers (1985), A Connecticut Yankee in King Arthur's Court (1989), Fatherland (1994) for which she won a CableACE award for supporting actress, and The Pale Horse (1997).

Marsh reprised her role as Rose Buck, who had returned to London to run an agency for domestic servants after a period spent nursing her mother in Suffolk.

[citation needed] Subsequently, a six-part second series was commissioned, and began transmission in February 2012 with Marsh's character appearing less frequently due to the stroke suffered by the actress.

[8] On 3 October 2011, the BBC announced that Marsh had suffered a minor stroke and would miss the beginning of the second series of Upstairs, Downstairs.

[9] Marsh was appointed Officer of the Order of the British Empire (OBE) in the 2012 Birthday Honours for services to drama.