Fernando spent two years in Istanbul after being discarded by City and the 31-year-old will reportedly cost Sevilla €4.5 million ($5 million/£4.04 million), signing a three-year contract.
The Brazilian originally signed with Manchester City in 2014 after proving a mainstay with Porto, as he made 236 appearances across six campaigns with the Portuguese club while winning four league titles and a Europa League crown during his time with the team.
He joined City following the team's Premier League title under Manuel Pellegrini, and would make 33 appearances in his first season as well as 42 during his second.
But playing time became harder to come by in his third campaign in Manchester as Fernando appeared just 22 times under Pep Guardiola in his first season in charge, prompting a move to Galatasaray in the summer of 2017.
During his time in Manchester, Fernando won just one trophy: the 2015-16 League Cup as City topped Liverpool in the tournament finale.
According to reports, Galatasaray were reticent to sell the Brazilian, but ultimately caved after Sevilla sporting director Monchi met the midfielder's agent Jorge Mendes, with the Turkish giants said to have reportedly owed Fernando part of his salary.
Fernando is the eighth new face to arrive at Sevilla in a busy transfer window, following Munas Dabbur, Jules Kounde, Diego Carlos, Lucas Ocampos, Joan Jordan, Luuk de Jong and Sergio Reguilon, while Maximilian Wober's loan from Ajax also became permanent.
There are likely to be further arrivals as well, while Sergio Rico, Sergi Gomez, Simon Kjaer, Joris Gnagnon, Guilherme Arana, Sebastien Corchia, Roque Mesa, Aleix Vidal, Ibrahim Amadou and Nolito could be sold.
Sevilla finished sixth in La Liga last term after finishing seventh the year prior, qualifying for the Europa League, a competition they have won a record five times.
The club's last Europa League triumph came in in 2016, when Sevilla completed a competition three-peat after previously winning the tournament in each of the prior two seasons.
Sevilla made it to the round of 16 in this year's tournament, where they were stunned by Slavia Prague 6-5 on aggregate.