The Spaniard, who made 17 appearances in Sky Bet League Two during a loan spell at Forest Green Rovers last season, will step up a division after sealing a move to the Crown Oil Arena.
The 21-year-old joined Albion in June 2015 from Spanish club Levante, before establishing himself as first choice in the club’s under-23s for the start of the 2016/17 Premier League 2 campaign.
The following season saw Sanchez help Simon Rusk’s side win promotion to the top tier, and his form for the Seagulls attracted a loan move to Forest Green.
Sanchez returned to Albion for the second half of the 2018/19 campaign, and found himself on the bench for Emirates FA Cup matches against West Bromwich Albion and Derby County.