Initially founded as a studio project in the year 2000 at Kraków by vocalist and multi-instrumentalist Mikołaj "M." Żentara with the collaboration of drummer Dariusz "Daren" Piper, both originally from the band Kriegsmaschine, together they recorded 2 unreleased demos, a collaboration split album with Deathspell Omega, Clandestine Blaze, Stabat Mater, Exordium and Musta Surma and their first 2 EPs. Daren left the band in 2006 and was replaced by Maciej "Darkside" Kowalski. The band signed to Northern Heritage Records in 2008 and have released all their full length albums to date with that label.
In 2012 after the release of With Hearts Toward None the band started touring worldwide, they enlisted bassist The Fall and guitarist Silencer, originally from Black metal band Medico Peste, to complete their live lineup. In 2015 Silencer left the band and was replaced by E.V.T., also from Medico Peste, as live guitarist. The tour, which helped the band to gain notoriety, had various notable performances at well known metal festivals like Nidrosian Black Mass on Belgium, Brutal Assault on the Czech Republic and Dark Easter Metal Meeting and Party San on Germany. During the same year M. and Darkside created "No Solace"; a label and mailorder in which they catalogue the music from Mgła and other projects. Through "No Solace" M. and Darkside also release music under the Kriegsmaschine moniker. From 2015 to 2016, the band's lineup joined Mikko Aspa's Clandestine Blaze for various shows.
In October 21, 2018 alongside the release of the third Kriegsmaschine album, the band announced they were working on their fourth studio album and that it would be released in 2019. On August 3, 2019 the band revealed that their fourth album would be titled Age of Excuse and released the track "Age of Excuse II" on the No Solace YouTube channel. Age of Excuse was released on September 2, 2019 on the band's Bandcamp and on CD through their label No Solace, they also announced that the album will be released on vinyl and that they would also upload the album on music streaming platforms in the following days. The band announced a European tour that would last throughout September in support of the new album, they will also embark on their first Latin American tour on 2020.
In April 2019 the band went on a European tour with Revenge alongside guest bands Doombringer and Deus Mortem which was marred with controversy and two cancelled shows on Munich and Berlin after the German Antifa group "Linkes Bündnis gegen Antisemitismus München" (English: Left Alliance Against Anti-Semitism Munich) launched a boycott against Mgła because of their alleged associations to various National Socialist black metal or "NSBM" artists and accusing them of racism and Anti-Semitism. The group listed Mgła's association with Mikko Aspa, owner of the label Northern Heritage Records, who has long been accused of having extreme Far-right sympathies and ties with the NSBM scene on Finland and throughout Europe at large, the band's association with fellow Polish black metal band and tour mates Deus Mortem; which had members who on occasions played live with openly "NSBM" bands Honor and Infernal War as well as Mikołaj Żentara's past dark ambient project "Leichenhalle" in which one of its albums titled “Judenfrei” (English: Free of Jews) featured Anti-Semitic lyrics as evidence. Mgła have denied the accusations and proceeded to pursue legal action against "Linkes Bündnis" and the sites that published their accusations, which the band described as false, a coordinated smear campaign and "defamation in print", they also asked fans to share the "defamatory publications" to support their case while offering apologies and discounts on the band's web store to those who planned to attend the cancelled concerts.