His first two albums, High Top Mountain[10] and Metamodern Sounds in Country Music, were independently released in the US[11] in 2013 and 2014 and in Europe, through the British record label Loose.

[23][24][25] Simpson formed the country rock band Sunday Valley in 2004,[23] which played at the Pickathon festival in Portland, Oregon.

He credits his wife and friends with changing what he characterized as a hobbyist focus on songwriting and playing to convincing him to get serious about music as a potential career.

[22] After playing local open mics and gigs, Simpson returned to Sunday Valley, touring and making an album with the band and producer Duane Lundy.

Among the session musicians were Hargus "Pig" Robbins on piano and Robby Turner, a former guitarist for Waylon Jennings, on steel guitar.

[33] Stephen Thomas Erlewine of AllMusic rated High Top Mountain 31⁄2 stars out of 5, comparing its sound favorably to Waylon Jennings.

[32] Erik Ernst of the Milwaukee Journal-Sentinel also compared it to Jennings, saying that it had "rich vintage sounds, heartbreaking ballads, and juke-joint ramblers".

[13] Simpson made his US network television debut on July 14, 2014, on the Late Show with David Letterman, playing "Life of Sin".

[58] In January 2017, Simpson appeared on the Felicity Jones-hosted episode of Saturday Night Live, playing "Keep It Between the Lines" and "Call to Arms.

While on the road in 2017, he suffered from a relapse of substance abuse and depression, though after the tour's conclusion, he reconnected with his wife "in a very profound and intense way" and also devoted more time to his children.

[66] The title, Sound & Fury, was announced on July 21, 2019, at San Diego Comic-Con, with Simpson describing it as a "sleazy, steamy rock'n'roll record".

[71] In a 2020 interview, Simpson described Sound & Fury as a record born from "burnout," especially in reaction to his 2017 tours, as well as the realization that he had become disillusioned with the music industry.

[75] The album was Simpson's first collaboration with Thirty Tigers (a distribution label for independent artists), whom he began to work with after ending his contract with Elektra.

[76] The album was officially released through High Top Mountain Records, a label that Simpson owns, and it was marketed and distributed by Thirty Tigers.

"[82] The Ballad of Dood and Juanita concluded a five-album "arc" he had envisioned and previously committed to, consisting of his five main albums and minus the Cuttin' Grass series.

The moniker had been used in Simpsons' work several times before, including as the name of a production company for the Sound & Fury film and as an easter egg in the artwork to A Sailor's Guide to Earth.

[88] He secured his first substantial role the same year, appearing in several episodes of the CBS All Access television series One Dollar, in which he plays the part of Ken Fry, a laid-off steel mill worker who sells stolen goods.

[87] In 2019, he wrote and performed the theme song for Jim Jarmusch's horror-comedy movie The Dead Don't Die, in which he also appeared as "Sturgill Zombie".

[92] In 2021, Simpson was cast in Martin Scorsese's epic Western crime drama film Killers of the Flower Moon (2023) as bootlegger Henry Grammer, who was involved in the Osage Indian murders.

[93] In 2023, Simpson joined the cast for the third season of the HBO crime comedy The Righteous Gemstones playing Marshall, a member of a doomsday prepping militia.

[94] He sang a cover of "All the Gold in California" that was later released on the season's soundtrack under the name of his character Brother Marshall and the Choir of Fire.

[95] Simpson has also expressed an interest in screenwriting; during a 2020 interview, he stated that he was working on a "punk rock" reboot of the 1981 film An American Werewolf in London, as well as a script based on his experiences in the Navy.

"[96] Simpson cites Merle Haggard, Willie Nelson, Keith Whitley, and Marty Robbins as large influences on his music.

"[100] Country Music Television suggested that Simpson has "a voice that recalls Merle Haggard [and] guitar licks that bring Buck Owens to mind.

In a 2020 interview, he said that he had been pursuing his own forms of self-care, including cutting sugar from his diet, racing rally cars, participating in shooting ranges, and ignoring news regarding the 2020 presidential election.