Williams was born in Spain to Ghanaian parents and has played once for the Spanish national in a friendly game in 2016.
The 28-year-old was still eligible to represent the Black Stars nonetheless but revealed in October last year that he felt too attached to his country of birth to play for another national side.
However, Williams has had a change of heart, having spent part of his holidays in the West Africa country this summer.
In a video posted on his social media channels, Williams said: "Every step we take forward has its own meaning. An evolution. A glance into the future which leaves a trace itself. A legacy. My parents have raised me with values based on humility, respect and love."
"They have taught me to embrace life. In that constant quest to continue growing and working upon the pursuit of evolving personally and professionally as an individual."
"That's why I feel the moment has come for me to find my origins within myself and with Africa and Ghana which means so much to me and my family. I want to return a small part of everything it has given to us because Ghana has played a significant part of becoming who I am as a person, as a son and as a brother."
"Today a new challenge begins. From now on, I will defend Ghana's T-shirt with all my will whilst I give my best. I'm one of the Black Stars."
Williams holds the record for the most consecutive appearances in La Liga history, having featured in each of Bilbao's last 233 matches in the Spanish top flight.
Ghana are in the same group with Portugal, Uruguay and South Korea for the upcoming World Cup.
