Charenton, the asylum depicted in the film, was established in 1645 and still exists and is still in use, although it is now called the Esquirol Hospital (l'Hôpital Esquirol), named for Jean-Étienne Dominique Esquirol, a French psychiatrist who ran the hospital in the 19th Century.
Several lines in de Sade's play give the impression that Charlotte Corday was a royalist (as she was portrayed, for instance, in the British press at the time of her trial). In fact she belonged to a revolutionary sect, the Girondins, more moderate than Marat's.
Patrick Magee won the 1966 Tony Award (New York City) for Supporting or Features Actor in a Drama for "Marat/Sade" as Marquis de Sade recreating his role in this production.
The full title of the original Broadway play was "The Persecution and Assassination of Jean-Paul Marat as Performed by the Inmates of the Asylum of Charenton Under the Direction of the Marquis de Sade" which opened on December 27, 1965 at the Martin Beck Theatre and ran for 145 performances. Ian Richardson, Michael Williams, Clifford Rose, Glenda Jackson, Freddie Jones, Hugh Sullivan, John Hussey, William Morgan Sheppard, Jonathan Burn, Jeanette Landis, Paul Robert Langdon, John Steiner, James Mellor, Henry Woolf, John Harwood, Leon Lissek, Susan Williamson, Carol Raymont, Mary Allen, Robert Lloyd, Jacques Roux, Patrick Magee, Mark Jones, Brenda Kempner, Maroussia Frank, Tamara Fuerst, Lynn Pinkney, Ian Hogg, Ruth Baker, Michael Farnsworth, Guy Gordon, Michael Percival, Heather Canning, Jennifer Tudor, Tim Hardy, and Stanford Trowell recreated their stage roles in the movie version. The original play was written by Peter Weiss, with the English translation by Geoffrey Skelton.
Glenda Jackson was nominated for the 1966 Tony Award (New York City) for Supporting or Featured Actress in a Drama for "Marat/Sade" recreating the role in this filmed production.