He has also collaborated with his ex-partner Alex Somers and has contributed to the scores for the films How to Train Your Dragon and We Bought a Zoo.

Jónsi's song "Around Us" was used for the American promotional trailer for Studio Ghibli's film The Secret World of Arriety and was also included in FIFA 11, the soundtrack by EA Sports.

"Boy Lilikoi" and instrumental versions of "Tornado", "Sinking Friendships", and "Around Us" were all included in the 2011 documentary This Is What Love in Action Looks Like.

Jónsi's song "Grow Till Tall" was used by the Bluecoats Drum and Bugle Corps in their 2017 competitive program Jagged Line.

Jónsi recorded "Sticks and Stones" for the score to the 2010 film How to Train Your Dragon,[5] for which DreamWorks Animation released a music video on 17 December 2010.

In 2014, Jónsi co-wrote the song "Where No One Goes" for the sequel, How to Train Your Dragon 2, with the film's music composer John Powell.

Jónsi additionally wrote a rough demo (entitled "Mama's Boy") for the film, which was eventually replaced by "Flying with Mother".

The project "promises to explore the ramifications of ongoing environmental collapse to the oceans and its inhabitants.

[9] A post that appeared on Jónsi's official site on 26 May 2009 stated that the artist was working on a solo album that would feature predominantly acoustic music and string arrangements from classical composer Nico Muhly.

The album was set to be produced by Peter Katis (Interpol, The National, Tokyo Police Club).

The MP3 announced the title of the album to be Go and gave a worldwide release date of "the week of 5 April 2010" through Parlophone and XL Recordings.

The Go limited-edition box set also included Go Quiet, a 45-minute film, directed by Dean DeBlois (director of the Sigur Rós concert film Heima), that features all nine songs from the album performed acoustically at home in Reykjavík, over New Year 2010.

[15] Jónsi released another single, "Swill", for the album on 24 June 2020, with an accompanying music video directed by Barnaby Roper.

[16] Jónsi makes a guest appearance under the alias 'Frakkur' on track 13, "Skyscraper Heart", on Hi-Camp Meets Lo-Fi – Explosion Picture Score by Dip (1999) Jónsi provides vocal material on three collaborations with The Hafler Trio: Exactly As I Say (2004 CD; a separate limited edition of 111 copies also exists containing DVD and 5.1 surround sound) Exactly As I Am (2005 Double CD) Exactly As I Do (2005 Double CD) Jónsi makes a guest appearance on Tiësto's track "Kaleidoscope"[17] on his album of the same name, which was released on 6 October 2009.

Hopelandic (Vonlenska in Icelandic) is the 'invented language' in which Jónsi sings before lyrics are written to the vocals.

[20]Like a few other players of the bowed guitar, Jónsi plays mainly variations of the Les Paul.

"[25] He briefly followed a raw food diet, although he no longer practices this as he felt it hindered his social life and he was "getting antisocial" when on tour.

[27][28][29] He also exhibited a large-scale experiential artwork titled FLÓÐ at the National Nordic Museum in early 2023.