In 2009, Ólafur also formed an experimental techno project, entitled Kiasmos, with Janus Rasmussen from the Icelandic electro-pop band Bloodgroup, announcing his electronic debut album in 2014.

In 2013, Ólafur composed the score for the 2013 ITV series Broadchurch, for which he won the 2014 BAFTA TV Craft Award for Best Original Music.

[4] In 2004, Ólafur composed and recorded the intro and two outros for tracks on the album Antigone by German metal band Heaven Shall Burn.

Being a huge fan, I gave them a demo with some very overly dramatic prog-rock songs I had been making at home – it was not so classic like this but had some badly computerized strings and piano in it.

A few months later they contacted me asked if I would write some intros and outros for their new album, but only with the piano/strings elements – So I wrote my first classical pieces.

In the same year, Ólafur toured with Sigur Rós and his second collaboration with Heaven Shall Burn, the album Iconoclast (Part 1: The Final Resistance), was released.

[6] Also in 2009, Ólafur formed an experimental techno project, Kiasmos, with Janus Rasmussen from the Icelandic electro-pop band Bloodgroup.

They released a joint EP with Ryan Lee West of the EDM project Rival Consoles entitled 65/Milo.

[9] The project was released as an album on 23 December 2011 and a corresponding short film, offered a rare glimpse into Ólafur's creative process and the close-knit musical community he is a part of.

More recently, he composed the score and end-credits track for the 2013 ITV series Broadchurch (again featuring the vocals of Arnór Dan[15][16]), for which he won the 2014 BAFTA TV Craft Award for Best Original Music.

Arnalds chose a program of Chopin works to create an emotional arc throughout the album and then composed linking sections for string quintet, piano, and synthesizer based on the atmosphere and motifs of those pieces.

She passed away a few hours later.”[21] In 2015, Ólafur's collaborations with Nils Frahm, Life Story Love and Glory (a completely improvised recording) and Loon, were collected on a double CD entitled Collaborative Works along with 2012's Stare and a live improvisational film entitled Trance Frendz - An evening with Ólafur Arnalds and Nils Frahm.

In June 2016 Ólafur announced his Island Songs[23] project, which would involve him working with director Baldvin Z and travelling to seven different locations in Iceland over seven weeks, collaborating with seven different artists.

In 2016, Ólafur and Quarashi frontman Sölvi Blöndal founded the record label Alda Music, which was acquired by INgrooves in January 2022.

On 18 October 2023, Ólafur hosted the official OPIA Community launch event titled 'OPIA Night' at Silent Green in Berlin, Germany.

The event featured several artists who Ólafur met online during the pandemic and have since been signed to the OPIA Community record label, including JFDR and Sofi Paez.

[27] Ólafur's favourite classical composers are Frédéric Chopin, David Lang, Shostakovich and Arvo Pärt.