Grant received critical acclaim for his role as Jack Hock in Marielle Heller's drama film Can You Ever Forgive Me?

Grant is also known for his roles in the feature films Warlock (1989), Henry & June (1990), Hudson Hawk (1991), Bram Stoker's Dracula (1992), The Age of Innocence (1993), The Portrait of a Lady (1996), The Little Vampire (2000), Gosford Park (2001), Penelope (2006), The Iron Lady (2011), Jackie (2016), Star Wars: The Rise of Skywalker (2019), and Saltburn (2023).

He is also known for his roles in television, including Frasier (2004), Dig (2015), Game of Thrones (2016), Hang Ups (2018), A Series of Unfortunate Events (2019), and Suspect (2022).

When Grant was 10, he witnessed, sitting in the back seat, his mother commit adultery in a car with his father's best friend, which subsequently led to his parents' divorce.

[13] He adopted his stage name (truncating his Afrikaans-sounding surname to a single letter) when he moved to Britain in 1982, a year after his father's death, and registered with Equity.

Since then, Grant has had supporting roles in the films Henry & June, L.A. Story, The Player, Bram Stoker's Dracula, The Age of Innocence, The Portrait of a Lady, Spice World, Gosford Park, Bright Young Things, and Penelope.

Martin wrote: "I kept these faxes, which grew to a stack more than 2 inches thick, because they entertained me, and because I thought they were valuable aesthetic chunks from a screeching mind, a stream-of-consciousness faucet spewing sentences – sometimes a mile long – none of it rewritten, and bearing just the right amount of acid and alkaline.

"[16] In 1995, Grant starred as the titular character in Peter Capaldi's short film Franz Kafka's It's a Wonderful Life.

[17] He made his first official Doctor Who appearance in the 2012 Christmas special, titled "The Snowmen", in which he plays the villain, Walter Simeon.

Grant appeared as "The Voice" in 2+2+2 at American Nights at The King's Head Theatre, from 3 to 29 July 2007, and in 2008 co-starred in the London-based comedy Filth and Wisdom.

This appearance followed Grant's involvement with the band the previous year, in which he spoke the lyrics to "This City" to background music as part of the intro and outro tracks on their only album, Theories of Dr Lovelock.

It recounted the story of how British Ministry of Defence Intelligence expert Jones had tried to warn that his government's September Dossier on Iraq's Weapons of Mass Destruction was inaccurate.

In 2023 he was cast in Emerald Fennell's psychological thriller Saltburn opposite Barry Keoghan, Jacob Elordi, and Rosamund Pike.

The film took him over seven years to complete[29] and starred Nicholas Hoult in the lead role, with Gabriel Byrne, Miranda Richardson, Julie Walters, and Emily Watson.

The book received positive reviews from critics, many of whom were impressed by the honesty of the tale, especially in regard to his difficult relationship with the "inexperienced" producer Marie-Castille Mention-Schaar.

During an interview with an Australian chat show, he mentioned that Wah-Wah was not released in France, and as a result, his producer did not make money out of it.

[34] Grant married voice coach Joan Washington in 1986 and had two daughters with her, Tiffany who lived for only half an hour and Olivia, and a stepson, Tom.