The 26-year-old arrived at Anfield from Celta Viga in June 2013 for £7.2million but is heading back to Spain after just one season in the Premier League.
Sevilla also have the option to sign Aspas on a permanent deal.
Aspas started just six matches for Liverpool last season and scored his only competitive goal for the team in the 2-0 victory over Oldham in the FA Cup.
Liverpool chief executive Ian Ayre travelled to Spain to conduct negotiations with Sevilla and agree the loan switch.
During his previous spell in Spain with Celta Vigo, Aspas scored 46 goals in 136 appearances for the club.