Iñaki Williams was born in Bilbao to Liberian parents who had immigrated to the Basque Country. At a very young age they moved to Pamplona where he would join the local youth academy of CD Pamplona where he was discovered by scouts from Athletic Club. He joined Lezama in 2012 at the age of 18 and was incorporated into the Juvenil A team where he scored 36 goals in his first season. He was promoted to Bilbao Athletic in 2014 and it quickly became clear that he was destined for great things as he lit up the league. He was handed his debut on 6 December, 2014 and scored his first goal just two months later in a Europa League match against Torino, becoming the first black player to score a goal for Athletic. Iñaki has since become a staple in the starting lineup which attracted attention from other clubs, but has responded by signing multiple contract renewals. The forward has said on numerous occasions that Athletic is his home and he wants to become a legend at the San Mamés.
Iñaki Williams is under contract through 2028 and his deal contains a €135 million release clause.