On 16 October 2018, Jackson's documentary about the First World War, They Shall Not Grow Old, was premiered as the Special Presentation at the BFI London Film Festival and followed by a question-and-answer session hosted by English film critic Mark Kermode. The film was created using original footage from Imperial War Museums' extensive archive, much of it previously unseen, alongside BBC and IWM interviews with servicemen who fought in the conflict. The majority of the footage (save for the start and end sections) has been colourised, converted to 3D and transformed with modern production techniques to present detail never seen before.
Before the screening, Jackson said, "This is not a story of the First World War, it is not a historical story, it may not even be entirely accurate but it's the memories of the men who fought – they're just giving their impressions of what it was like to be a soldier."
Reviewing the film for The Guardian, critic Peter Bradshaw said:
To mark the centenary of the First World War's end, Peter Jackson has created a visually staggering thought experiment; an immersive deep-dive into what it was like for ordinary British soldiers on the western front. This he has done using state-of-the-art digital technology to restore flickery old black-and-white archive footage of the servicemen's life in training and in the trenches. He has colourised it, sharpened it, put it in 3D, and, as well as using diaries and letters for narrative voiceover, he has used lip-readers to help dub in what the men are actually saying.
The effect is electrifying. The soldiers are returned to an eerie, hyperreal kind of life in front of our eyes, like ghosts or figures summoned up in a séance. The faces are unforgettable.
The film was broadcast on BBC Two on 11 November 2018 (the hundredth anniversary of the Armistice of World War I), earning acclaim for its restoration work, immersive atmosphere, and portrayal of war. To accompany the film, a special episode of the documentary series What Do Artists Do All Day?, which followed Peter Jackson making the film, aired the following day on BBC Four.
In October 2016, Jackson, who had announced his interest in a film adaptation of the novel Mortal Engines in 2009, stated that the film would be his next project as producer and co-writer, once again alongside Fran Walsh and Philippa Boyens. The film was directed by his long-time collaborator Christian Rivers. It stars Robert Sheehan, Hera Hilmar, Hugo Weaving, Jihae, Leila George, Ronan Raftery, and Stephen Lang. It premiered on 27 November 2018 in London, received negative reviews and was a box-office bomb.
On 30 January 2019, the fiftieth anniversary of the Beatles' rooftop concert, which was the band's final performance, Jackson announced that his next directorial work would be a documentary about the making of their final album Let It Be. In a process similar to his previous documentary project They Shall Not Grow Old, this created around "55 hours of never-before-seen footage and 140 hours of audio made available to [Jackson's team]", which are "the only footage of any note that documents them at work in the studio". The documentary used the techniques developed for They Shall Not Grow Old to transform the footage with modern production techniques, and seeks to display a new side of a period in the Beatles' history usually remembered as highly conflictual. Most of the used footage was originally recorded for the 1970 Let It Be documentary.
Clare Olssen and Jabez Olssen, respectively producer and editor of They Shall Not Grow Old, returned for this new project, with Ken Kamins, Jeff Jones and Jonathan Clyde as executive producers. The project was made with "the full co-operation" of Paul McCartney and Ringo Starr, the last two living Beatles, as well as John Lennon and George Harrison's widows Yoko Ono and Olivia Harrison. The film includes the full 42-minute last rooftop concert.
In March 2020, Walt Disney Studios announced they had acquired the worldwide distribution rights to Jackson's documentary, now titled The Beatles: Get Back (the name of a track featured on Let It Be, and the originally-planned name for the album). It was originally set to be released by Walt Disney Studios Motion Pictures on 27 August 2021 in the US and Canada with a subsequent global release to follow. In June 2021, it was announced that it would be released on Disney+ as a three-part documentary series on 25, 26 and 27 November 2021. The documentary was released to critical acclaim, and won five Primetime Emmy Awards, including Outstanding Documentary or Nonfiction Series and Primetime Emmy Award for Outstanding Directing for a Documentary/Nonfiction Program for Jackson.
The "de-mixing" technology developed to isolate instruments and vocals from old audio recordings to achieve a better sound quality in Get Back would have an effect on Beatles records themselves: Revolver: Special Edition, a 2022 reissue of the band's 1966 album Revolver, would use the technology to improve the album's audio quality. Annie Zaleski of The Guardian, who gave Special Edition a five out of five stars rating, wrote that: "new details tease out deeper meanings in the songs. Now more prominent, the low-lit backing harmonies on 'Here, There and Everywhere' remake the tune as an old-fashioned rock'n'roll love song; the piano bending out of key on 'I Want to Tell You' mirrors the narrator's insecurity; and McCartney's booming walking bass on 'Taxman' illuminates the biting, cynical tone of Harrison's lyrics... Revolver still sounds so vibrant." It would eventually lead to the release on 2 November 2023 of "Now and Then", dubbed "the last Beatles song", which used the technology to salvage audio from a 1977 demo by Lennon and a failed 1995 attempt by the other three ex-Beatles to complete the song (Lennon having been murdered in 1980), together with newly recorded music by McCartney and Starr, to finally release the song over 55 years after it was first conceived. The short documentary film Now and Then – The Last Beatles Song, featuring Jackson, chronicled the making of the song. "Now and Then" received received widespread attention and acclaim upon release, winning a Grammy Award and being considered a worthy finale for the Beatles.
Jackson personally directed the "Now and Then" music video, using new footage of McCartney and Starr and using restored old footage similarly to Get Back to have all four Beatles visually on-screen. In an interview days before the song's release, Jackson claimed that he had originally been "very reluctant" when offered to direct the video, but that McCartney, Starr and Apple "didn't even wait for me to say no" before proceeding to send him footage for the video. I found myself swept along as they quickly addressed my concerns. Paul and Ringo shot footage of themselves performing and sent that to me." He stated that he made the video thinking of it as a short film rather than a music video. The video was met with a mixed response, with praise for its emotional weight but criticism for the inclusion of the dead Harrison and Lennon into more recent footage.
