Gomez, 32, joined Atalanta from Metalist Kharkiv in 2014 and was a key factor in the club's rise from mid-table also-ran to regular top-four challenger.
He became captain in 2017 after a personal-best haul of 16 Serie A goals in 2016-2017, before capaining the club to its highest-ever top-flight finish of third in 2018-2019.
Atalanta repeated the feat in 2019-2020 and Gomez, whose 16 assists was the most by any player in a single Serie A season this century, was named the league's best midfielder in the end-of-season awards.
Gomez and coach Gian Piero Gasperini reportedly fell out earlier this season, with Italian media claiming the player had refused to carry out the manager's orders in the 1-1 Champions League draw with Midtjylland.
Speculation was rife throughout December about whether the pair would be able to repair their relationship or if Gomez was on his way out, with Inter initially thought to be his likeliest of options.
More recently Italian publications suggested Atalanta was keen to offload him to a foreign team, and Sevilla – whom Gomez had previously suggested was his favourite Spanish team – made its move.
The talented attacker, who can play on the left flank or behind the striker, signed a contract until June 2024 on Tuesday.
He is an Argentina team-mate of current Sevilla players Lucas Ocampos and Marcos Acuna, and was given his Albiceleste bow by the club's former coach Jorge Sampaoli.
Sevilla will hope Gomez can serve its as effectively he did Atalanta in the main – from the start of 2018-2019 until 16 December, when he last featured in Serie A for the Bergamo side, no player across Europe's big five leagues played more key passes than his 233.
Similarly, his 29 assists across the same period was bettered by only Thomas Muller (36), Lionel Messi (34) and Jadon Sancho (33). There were also only five players to create more Opta-defined "big chances" than his 40 in that time.