Although Walt Disney initially purchased the film rights to The Ill-Made Knight in 1944, he eventually produced an adaptation of The Sword in the Stone, released in 1963. This movie reflects more the sense of humour of Disney's team of animators than White's. The movie adds a more comical side to the original story, including song and dance, as in most Walt Disney films. Alan Jay Lerner and Frederick Loewe's 1960 musical Camelot (which was made into a movie in 1967) is based mostly on the last two books of The Once and Future King, and features White's idea of having Thomas Malory make a cameo appearance at the end, again as "Tom of Warwick".
BBC Radio 4 serialised the book in six one-hour episodes dramatised by Brian Sibley beginning on Sunday 9 November 2014 with Paul Ready as Arthur and David Warner as Merlyn.
- In the Marvel Universe, the X-Men comics mention The Once and Future King several times, notably in the first issue of the "X-Tinction Agenda" story arc, which mentions that the book is Professor X's favorite, and that Xavier always saw himself as Merlin, the teacher guiding the hero(es), rather than as a hero himself. In the Ultimate X-Men comics, the book is a metaphor for Magneto, an extremely powerful mutant terrorist. This is carried over into the 2003 film X2: X-Men United, which begins one scene with Magneto reading the first edition of The Once and Future King in his prison cell. At the end of the film, Xavier is using the book as a teaching tool. It is mentioned again in Ultimate Comics Spider-Man.
- In Rodman Philbrick's "Freak the Mighty", Max Kane and Kevin Dillon bond through the book; and, inspired by Dillon's fits of fancy, the two embark on a quest to embody the heroic qualities of King Arthur.
- In Bobby (2006) Edward Robinson (Laurence Fishburne) relates the novel's depiction of King Arthur to the selfless and chivalrous qualities of Jose Rojas (Freddy Rodriguez).
- The Magicians by Lev Grossman includes a long sequence where magicians-in-training are transformed into geese, a "direct and loving homage" to Wart's transformation in The Sword in the Stone.
- George A. Romero's film Knightriders references The Once and Future King as the inspiration for a traveling Camelot of motorcycle-riding knights aspiring to the code of chivalry.
- The animated series Gargoyles references The Once and Future King when King Arthur is awakened in Avalon.
- The TV series Merlin talks about The Once and Future King throughout the series, the first time said by the Great Dragon to Merlin about his destiny.
- The film The World's End draws heavily on White's work, with aspects of the story mirroring Arthurian legends and the main character, Gary King, referring to himself early on as "the once and future King".