Recorded at the band's studio in New York City, it was produced by lead vocalist Joe Duplantier, mixed by Andy Wallace and mastered by Ted Jensen.

Gojira's ambition was to write a more cohesive and brighter album than Magma, emphasizing a progressive sound while incorporating guitar solos and classic rock elements with a positive lyrical message.

To promote the album, Gojira was scheduled to embark on their first arena-level headlining tour in 2022 in Europe and the UK, but it was postponed due to varying COVID-19 restrictions.

Having had sustained requests to tour worldwide in support of Magma, beyond the initial cycle, Gojira declined in order to focus on writing a new album.

[1] The album's songwriting officially started in early 2018 at New York's Silver Cord Studio, which would become "the cocoon for a two-year creative odyssey".

[5] While retaining their signature style, Gojira extended their range to a "traditional dimension" and started sliding their sound towards the 1970s and 1980s major chords–progressions of "classic bands", embracing melodies and guitar solos.

[2][8] On Fortitude, the band put forward the use of backing vocals and choirs that were already present on the previous albums but "buried" in the mix.

[3][1] Meanwhile, Joe Duplantier, a New York State resident, was visiting his father in southwest France, which complicated the mixing process.

Then Joe Duplantier spent several months in a cabin in the Landes forest without listening to the new tracks and forsook his cell phone and computer.

He would prefer to be left alone in the studio, without assistants, being vulnerable to coronavirus infection due to his age, saying he was "infinitely upset not to be with the band".

[15] Wallace retained the desire for a raw rendering and the integrity of the spontaneity of Gojira's compositions while bringing "warmth" to the instrumentation.

[3][1] Combining the direct approach of The Way of All Flesh mingled with the atmospheric arrangements of Magma, the structure of the songs provided the album an immediacy and more accessibility while offering a return to heaviness.

[25] "Amazonia" features a "massive bass groove" from Jean-Michel Labadie along with the interactive playing of guitarists Christian Andreu and Joe Duplantier.

's Sam Law noted a British influence on "Hold On",[3] while AllMusic's Thom Jurek echoed this view and compared it to Black Sabbath.

[22] Law described "The Chant" as "chain-gang blues, bayou gospel, bar-room Americana",[3] while Spin felt that Gojira took "some risks" with the song, which includes jangly guitar sound and clean vocals.

[27] The "heaviness" stood out on the album, according to Metal Hammer; "Grind" contains an abundance of Gojira's trademark pick-scrapes, while "Sphinx" features guttural vocals thus correlated to The Way Of All Flesh.

[26] The shifting rhythms showcase Mario Duplantier's trademark drumming style throughout Fortitude amid "death metal grooves" and blast beats, while "Grind" was described as "heavy, syncopated, technical, and nuanced in production, with raging vocals".

[22] Spin summed up the album's sound as "generally lighter and more accessible, leaning on elements of prog and classic rock" and noted that it was "a far cry from the searing technical death metal that fueled the band a decade ago".

[27] Jonathan Horsley of Guitar World wrote that the album's accent was deliberately on prog and post-metal and also nuanced by electronic elements.

[32] Reflecting later on his state of mind while writing the lyrics, Joe Duplantier observed: "In an uncertain world, chaotic, I choose optimism by default.

"[5] Joe Duplantier had been immersing himself in Tibetan and Thai philosophy, which were a source of inspiration for the lyrics of "Born for One Thing", conveying an anti-consumerist message.

[33][34] The lyrics to "Amazonia" chronicles the reckless deforestation that has accelerated in Brazil under the reign of Jair Bolsonaro,[35] shown in the lines, "The greatest miracle is burning to the ground".

[36] Gojira launched the charity auction on the Propeller platform through a call for solidarity from metal bands such as Metallica, Tool, Slayer, Slash, Sepultura, Deftones, Lamb of God, among others.

[47] Joseph Schafer, writing for Consequence, stated: "Gojira have developed into one of modern metal's premier bands, delivering strong LPs throughout their career, but new album Fortitude makes some bold moves that might help them reach an even wider audience."

[53] Forbes termed Fortitude as a demonstration of a "strong sense of urgency felt on the number of social–political issues that Gojira highlight", and praised "these haunting yet poignant lyrical themes.

's Paul Travers wrote that "Gojira never seemed like a band built for the mainstream", but that Fortitude "sounds like the album that could propel them the rest of the way to the top."

"[16] Loudwire described Fortitude as a "dynamic and thought-provoking collection of groove metal beatdowns" while the band "explores a wide range of warm tones throughout the album's mix".

[55] Olivier Ducruix of Montreuil's Guitar Part magazine praised "the incredible richness of this record" and wrote that "The riff machine is running at full speed here.

He also noted that the band embraced a far proggier approach than previous albums and was also aiming for the mainstream like Mastodon's 2009 Crack the Skye.

[112] On 30 August 2022, a riot broke out at the Caupolicán Theatre entrance in Chile when 80 fans attempted to enter the venue during Gojira's show, which had sold out in less than 24 hours.