The fee becomes the second highest Spurs have ever paid for a player since shelling out £58.8 million for Tanguy Ndombele in 2019.
Romero was part of the Argentina squad that won the 2021 Copa America title in Brazil, a first major title for the Albeactes in many years.
With his impressive performances for Atalanta, Romero attracted interest from several clubs but Spurs have finally landed his services.
Spurs after completing the signing of Romero said in a statement;
"We are delighted to announce the signing of Cristian Romero from Atalanta.
Cristian will wear the number four shirt."
The 23-year-old insists he is "ready to start and give everything" for his new club.
"I'm very happy to be wearing this shirt and to come to this club," he said.
"I want to thank the fans for all the messages. You wanted me here and here I am."
Atalanta also thanked Romero for his "unforgettable" 2020-21 season.
"He scored decisive goals and provided crucial assists, and above all he [has] always worn our shirt with commitment, dedication and passion," Atalanta said.
Romero becomes third summer signing for Spurs following the arrivals of Bryan Gil and Pierluigi Gollini from Sevilla and Atalanta respectively.
Atalanta have replaced departed Romero with the signing of Juventus defender Merih Demiral on a season long loan.
Romero scored 2 goals in thirty-one Serie A games with two assists for Atalanta last season as he helped Gian Piero Gasperini's side to finish third in the league log.
