The midfielder will be wearing the no.6 shirt at the Amsterdam-based club for the next two and a half years.
Henderson, who was playing in the Saudi Pro League for the past six months, is back in European football.
“Amsterdam! So happy to be here. Can't wait to see you all soon," Henderson posted on social media platform X.
Ajax Life stated online that the club record has been broken for shirts of a single player sold within 24 hours.