He speaks fluent Spanish. In addition to a brief scene in Friends with Money (2006), his role in The Conspiracy (2008) (original title: 'La conjura de El Escorial') was entirely in Spanish.
He writes left-handed but otherwise uses his right hand.
He has a daughter named Ruby, born in August 2005, who was named by her older sister Lily.
He is a passionate comic book fan and had an enormous Marvel and DC collection in his childhood.
He has a daughter named Lily, born on 23 March 2002.
He met his wife Emma Hewitt at drama school.
Both of his parents came from Ashkenazi Jewish families. His ancestors emigrated to England from Belarus, Russia and Poland, settling mostly in Liverpool.
Emma Hewitt is his unmarried partner, with whom he has lived for 20 years.
He has a cult following thanks to BBC Radio Five Live's weekly 'Kermode and Mayo's Film Review', where he is regularly greeted by his former classmate and film critic Dr Mark Kermode ("Hello to Jason Isaacs!"), a practice adopted by the show's fan base.
Harry Potter star Gary Oldman is one of his favourite actors.
He is the long-time best friend of writer/director Paul W. S. Anderson.
He was ranked 54th on Empire Magazine's list of the 100 Sexiest Movie Stars.
He was set to play Dr. William Birkin in Resident Evil: Apocalypse (2004) but left the project.
Girard Swan worked as Mel Gibson's stunt double as well as Isaacs's stunt double and double on The Patriot (2000).
In Peter Pan (2003) he sings two songs (albeit briefly). (Isaacs was also listed for these songs in the end credits; however, the songs themselves were cut from the soundtrack. His other film singing performances (not listed in the credits) were in The Last Minute (2001) (two songs) and Sweetwater (2013). On TV (BBC), Isaacs sang in the 2013 episode of Case Histories (2011), 'Jackson and the Women' (2013), and in the BBC Four TV play The Curse of Steptoe (2008). These too were not listed in the credits.)
He shares two roles with Hans Conried. Conried appeared in the Disney animated version of Peter Pan (1953), while Isaacs appeared in the 2003 live-action film. Both films followed a tradition encouraged by J. M. Barrie and followed in most stage productions, in which Mr Darling and Captain Hook are played by the same actor. Accordingly, he and Conried both played both roles in their respective films.
He is depicted as the character Captain Lorca on one of a set of 18 British commemorative postage stamps issued on 13 November 2020 celebrating the "Star Trek" television and film series. The stamps were issued as 12 separate stamps honouring captains and crew members, and 6 stamps on a single commemorative sheet highlighting heroes and villains. All the stamps were denominationless and marked as first class (76p on the day of issue). Others honoured with this set include William Shatner, Patrick Stewart, Avery Brooks, Kate Mulgrew, Scott Bakula, Leonard Nimoy, Marina Sirtis, Alexander Siddig, Dominic Keating, Sonequa Martin-Green, Shazad Latif, Simon Pegg, Tom Hardy, Malcolm McDowell, David Warner, Alice Eve and Idris Elba.
Isaacs worked with Logan Lerman twice: in The Patriot (2000), where they were Colonel William Tavington and William Martin respectively; and in Fury (2014), in which Isaacs played Captain Waggoner and Lerman played Norman Ellison.
He has played both Superman and his arch-enemy Lex Luthor, voicing Superman in Superman: Red Son (2020) and Lex Luthor in Justice League: Gods and Monsters (2015).
In Armageddon (1998), Harry Stamper (Bruce Willis) sarcastically calls Dr. Ronald Quincy (Isaacs) "Mr. Wizard". Four years later, Isaacs began playing Lucius Malfoy, who is in fact a wizard (in Harry Potter and the Chamber of Secrets (2002)).
He is good friends with Paul Greengrass.
He has appeared in at least two films alongside the children of music legends. In Armageddon (1998) he appeared with Liv Tyler (daughter of Aerosmith's Steven Tyler). Lily Collins, daughter of Genesis drummer/singer Phil Collins, appeared in Abduction (2011), in which Isaacs also appeared.
Isaacs has made two films in which Joseph Stalin is portrayed: Adrian McLoughlin played Stalin in the black comedy The Death of Stalin (2017), and William Salyers voiced Stalin in the direct-to-video Superman: Red Son (2020).
He has worked with two different men named "Paul Davies": Paul Davies was the Supervising Sound Editor on Isaacs's film 'Good' (2008). Paul Davies was an uncredited Assistant Colourist on both 'Black Hawk Down' (2001) (in which Isaacs played Captain Mike Steele) and the 2002 production 'Harry Potter and the Chamber of Secrets' (2002), as well as on the other "Harry Potter" films in which Isaacs's character Lucius Malfoy was introduced.
He graduated from the Central School of Speech and Drama.
He played identical twins in an episode of Taggart.
He appeared on stage at the Royal National Theatre in Angels in America.