Having left Paris St-Germain on a free transfer, the 37-year-old has signed a one-year deal.
"It's a very special day, returning home is always a tremendous joy," said Ramos, who returns to Sevilla with the club bottom of La Liga.
"I am happy to return and try to contribute as soon as possible, which is the important thing."
Ramos won a World Cup and two European Championships with Spain, earning a record 180 caps over 16 years, while also lifting four Champions League trophies with Real Madrid.
He grew up on the outskirts of Seville and joined the club's academy aged seven, going on to make 50 appearances in all competitions before signing for Real Madrid in 2005.
Ramos spent 16 seasons in the Spanish capital, racking up 671 appearances and winning 22 trophies, with five La Liga titles to go alongside his European success.
He joined PSG after his Real contract expired in 2021 and spent two seasons there, winning successive league titles.