After a decade of playing the violin at the local music school, Uddevalla, Sweden-born Eng picked up the guitar at age 14, and started writing songs a couple of years later. In 2007 he was part of a gaming forum initiative where users were challenged to make music based on the video game Portal. Eng wrote an acoustic ballad that caught the ear of Simon Flesser, who had just started the gaming studio Simogo. The studio was about to release its first game, and Flesser asked Eng to write a ballad in a similar style for the game’s trailer. That was the beginning of a long collaboration, as Eng contributed with songs for subsequent Simogo releases.
During 2014 Jonathan Eng composed the soundtrack for interactive narrative experience The Sailor’s Dream, consisting of a mix of instrumental tracks and a seven-part musical story told in folk song-form. The soundtrack earned him award nominations at the Independent Games Festival and The BAFTAs. In 2015 a spinoff radio drama based on The Sailor's Dream was released, for which Eng also composed and recorded the music. The same year he started working on songs for Simogo's "Project Night Road" together with composer and producer Daniel Olsén. The game was later revealed to be the rhythm-action pop album video game Sayonara Wild Hearts. Sayonara Wild Hearts and its soundtrack was released in 2019.