The band had its initial beginnings in 2015[1] when Jacob Charlton, Ben Maida, Sam Anderson and Ethan McCann began performing in Battle of the Bands competitions[2] whilst at high-school at Vermont Secondary College in outer suburban Melbourne.

The band's first formal release occurred in 2016 with debut single "XY" on 2 June 2016, featuring Void of Vision's Jack Bergin.

The band's first ever headline show premiering Butterfly live followed on 7 April at the Melbourne venue, Cherry Bar, to a sold-out crowd.

[13] Thornhill embarked on a series of shows throughout 2018 and early 2019, supporting bands for Australian tours including Ocean Grove, Make Them Suffer and In Hearts Wake.

The Dark Pool gained widespread attention leading to publicity with rock and heavy-metal focused journals and news sites.

[25] The Dark Pool was selected by Triple J as the station's 'Feature Album' for the first week of December 2019[26] In November, the band headlined 'Misery: Emo Boat Party', a nautical-inspired gig held on board 'The Lady Cutler', a cruising boat departing Melbourne where the members of the band dressed up in old seamen style outfits.

[30] On 5 April 2020 a glitch in Triple J Darwin's broadcast system saw Thornhill make headlines when track "Lily and the Moon" was accidentally played on public radio on-loop for nearly four hours from approximately 4:30 am to 8:30 am.

[32][33] On 5 February 2021 the band's lead singer, Jacob Charlton, featured on the single "Year of the Rat" (featuring Jacob Charlton) by Void of Vision, a rework of the band's original song from their 2019 album Hyperdaze.

[35] Unfortunately the band was caught in the middle of a COVID-19 outbreak in Brisbane at the time and was forced to return to Melbourne to quarantine, requiring the rescheduling of the rest of their tour planned for the Australian East Coast[36] Thornhill released the single "Casanova" on 28 October 2021, premiering on Triple J.

[39] On 16 September 2022, the band announced the cancellation of their upcoming October/November tour with August Burns Red, Bury Tomorrow, and Miss May I, citing feeling "mentally burnt out" recently, being "forced to consider the longevity of the band" in order to "recharge and be ready to go again in 2023".

[40] On 24 January 2023, the band revealed that their rehearsal space had been broken into and that $100,000 worth of personal belongings and musical equipment had been stolen.