"It's a very special day, returning home is always a tremendous joy, now we have to do the medical," Ramos, 37, told the media.
"Happy to return and try to contribute as soon as possible which is the important thing."
Sevilla sit bottom of La Liga without a point after three matches but as Europa League champions, have qualified for the Champions League group stage. They start their campaign on September 20.
Ramos left Sevilla at the age of 19 to join Real Madrid for a then record fee for a Spanish defender.
In 2021, Ramos signed for Paris Saint-Germain but had been without a club since his contract with the French champions ran out in June.
According to the local press, Ramos had a good offer from Al Ittihad in Saudi Arabia.
"I was eager to return home. It made no sense to go anywhere else without passing through here," said Ramos who was born on the outskirts of Seville.
In 16 seasons at the Bernabeu, Ramos won La Liga five times, the Champions League four times and the Champions League four times.
He played 180 games for Spain, scoring 23 goals, and was part of the team that won the European Championship twice (2008 and 2012) and the 2010 World Cup in South Africa.
