The Ghana Football Association confirmed that the Brighton wing-back, who had represented England at different youth levels and made two appearances for the Under-21s, had opted to play for the Black Stars.
He will be available for selection at the World Cup in Qatar, where Ghana will face South Korea, Portugal and Uruguay in Group D.
“We have always maintained that we will not limit ourselves to only a small group of players but would scout top talents across the globe who are ready to sacrifice for the nation and take us to the next level,” a Black Stars statement read.
The Athletic reported back in May that Lamptey had been in no rush to resolve his international future.
England had been desperate not to lose the 21-year-old but he requested to be left out of England’s Under-21 squad for last month’s European Championship qualifiers against the Czech Republic, Albania, Kosovo and Slovenia to focus on a big decision.
Lamptey qualifies for Ghana through his parents, with his father, Ahmed, a major influence, but the input of former Brighton boss Chris Hughton — a technical advisor for the Black Stars — is also understood to have been pivotal. It is understood that Hughton regards Lamptey not just as an attacking right-back but also as a right winger.
Athletic Bilbao’s Inaki Williams has also joined Lamptey in deciding to represent Ghana.
Players can switch national sides as they as long as they have played three senior appearances or fewer, and providing those appearances came before they were 21.
One of the most high-profile players to recently switch allegiance was Jamal Musiala, who chose to represent Germany, the country of his birth.