Nico Williams has been an important player in Athletic Bilbao's squad since making his debut on April 28, 2021.

In the 34th match week game against Valladolid in San Mamés, Marcelino García Toral gave the youngest of the Williams the opportunity to make his debut.

Coming on as a second-half substitute for Jon Morcillo in a 2–2 home draw against Real Valladolid; his brother Iñaki also came off the bench ten minutes later. It was the first time two siblings had been on the pitch at the same time for the club since Julio and Patxi Salinas in 1986.

Williams scored his first two goals for the Lions on 6 January 2022, in a 2–0 win over Atlético Mancha Real in the campaign's Copa del Rey. Seven days later, he scored the winning goal in a 2–1 victory over Atlético Madrid in the semi-final of the 2021–22 Supercopa de España.

Spanish national team coach Luis Enrique added Nico Williams to his World Cup squad after the youngster's fantastic performance for the Lions in La Liga. The pacey forward featured in four games for Spain in Qatar.