[2] After retiring he become a referee[3] and he was also an entrepreneur and owner of the family business called Confitería Prast, a confectionery founded by his father and which he took care of together with his brothers.

He was one of the main architects behind the team's football power in the 1900s, and was also one of the club's first goalscoring figures, becoming its all-time top scorer.

[6][a] He was a member of the historic Madrid FC side of the 1900s, which also included José Berraondo, Pedro Parages, the Yarza brothers (Manuel and Joaquín) and Federico Revuelto.

He also played three matches for Real Sociedad in the 1909–10 season[8] including one Copa del Rey match,[9] which was the final of the 1910 Copa del Rey (UECF) against Athletic Bilbao (Real Sociedad participated under the umbrella of a local club, Vasconia Sporting Club, due to regulations of the time) but unlike in his Madrid days, Prast was unable to impact the game and his side lost 1–0 thanks to a goal from Remigio Iza.

[10] The remaining two matches came in the inaugural edition of the Pyrenees Cup,featuring in the semi-finals against Stade toulousain at Ondarreta Stadium on 17 April as they won 8–0, and though they lost the final 2–1 to FC Barcelona,[8][11] it was he who scored Sociedad's consolation goal in the 30th minute after a pass from George McGuinness.