Gorostiza was born in Santurtzi, Biscay. He played youth football for Chávarri de Sestao and Zugazarte, making his senior debuts with Arenas Club de Getxo and Racing de Ferrol (one season apiece), and signing for Athletic Bilbao in 1929. He made his La Liga debut on 1 December 1929 against Real Madrid, and scored 37 league goals in his first two seasons combined (only 36 games) as the club won back-to-back national championships, adding as many Copa del Rey trophies.
Gorostiza was a member of an Athletic team that also included Bata and was coached by English Fred Pentland, and won two Pichichi awards with the club. He scored the winning goal in the 1933 Spanish Cup final, a 2–1 win against Real Madrid in Barcelona.
During the Spanish Civil War, Gorostiza played with the Euskadi XI, a team which was put together at the suggestion of José Antonio Aguirre, the president of the Basque Country and a former Athletic player. The side went on tour to raise funds for the Basque cause and played in Europe and Mexico, even entering the Mexican league during the 1938–39 season.
Valencia / Later years
On returning to Spain in 1940, Gorostiza joined Valencia CF. The young Che squad had managed to remain intact during the conflict and now, aided by the veteran (31), eventually won two leagues and one cup, with the player netting in double digits in four of his six seasons, with a best of 20 goals in 24 games in 1941–42.
After leaving Valencia, Gorostiza played for Barakaldo CF during the 1946–47 season, in Segunda División, and then retired, at the age of 38. However, he twice came out of retirement, with CD Logroñés and Juvencia Trubia, finally calling it quits in 1951.
While at Athletic, Gorostiza made his debut for Spain, appearing against Czechoslovakia on 14 June 1930. He represented the nation at the 1934 FIFA World Cup, playing in the 3–1 win against Brazil and the 1–1 against Italy; he missed the replay against the latter, in a 0–1 loss.
- Athletic Bilbao:
- Pichichi Trophy: 1929–30, 1931–32
|1929/30||Athletic Bilbao||La Liga||18||20||10||9||8||4||36||33|
- De Gorostiza a Penev, pasando por Romario (From Gorostiza to Penev, with reference to Romario); Levante-EMV, 27 December 2009 (Spanish)
- Stats at Liga de Fútbol Profesional (Spanish)
- BDFutbol profile
- Athletic Bilbao profile
- National team data (Spanish)
- Guillermo Gorostiza at National-Football-Teams.com