Prieto started his professional career at Once Municipal for two years, before he joined historical club Alianza F.C.
where he played the majority of career, he was part of the team that conquered 1986-87 title.
After retiring from professional football, Prieto was appointed manager of Titán in 2008.
Prieto second spell at Titán was his most successful spell in his managerial career, winning 2 Segunda División Salvadorean titles (Apertura 2010, Apertura 2011), the club almost won promotion on both occasion, however the club lost both matches against Juventud Independiente and Santa Tecla F.C.
Following the club folding and being on hiatus for several years, Prieto joined Once Lobos and later re-joined the coaching staff at Alianza helping the team win .