Founded from the amalgamation of Real Unión Deportiva de Valladolid and Club Deportivo Español, the club played its first game on September 22, 1928. It was a win over Alavés 2:1. Valladolid first reached the top level in the 1947–48 season, as champions of the Segunda División. The club became the first Castile and León club to play in the Spanish top flight. the following year, the team pushed on from this success and reached the finals of the domestic cup in the Chamartín Stadium against Athletic Bilbao, losing 4–1.