The Nigeria international makes the switch to the Eredivisie, having moved to Glasgow for just under a £300,000 training compensation fee in the summer of 2020.
Ajax have announced the versatile 22-year-old defender has sgined a five-year contract, with the club paying €23m (£19.58m) rising to €26.5m (£22.5m) including potential add-ons.
Bassey has enjoyed a rapid career rise since leaving Premier League Leciester City after progressing through the club’s youth academy.
He quickly established himself as a regular first-choice starter under previous Light Blues boss Steven Gerrard and played a leading role in stopping Celtic from clinching ten-in-a-row during season 2020/21.
His development continued last season, helping his team mates to Scottish Cup glory at Hampden and starring in the club’s sensational run to the Europa League final in Seville.
Bassey, who will wear the number 33 shirt at Ajax, leaves Rangers having made 65 appearances in total.
A club statement read: “Rangers Football Club can today confirm Calvin Bassey has joined Ajax in a deal which is the largest in Rangers’ history.
“Calvin leaves with best wishes from everyone at Rangers and we thank him for his hard work and commitment over the past two seasons.
“The 22-year-old joined Rangers from Leicester City for a Training Compensation Fee in the summer of 2020, making 65 appearances for the Light Blues.
“Bassey played his part in Rangers’ historic 55th league title victory, won the 22 Scottish Cup, while also having a huge role in the incredible UEFA Europa League run to the final in Seville last season.
“We wish Calvin all the best for his future career.”
His departure follows the recent sale of attacking midfielder Joe Aribo, with Leon Balogun and Cedric Itten also leaving the club this summer in what has turned out to be a busy transfer window for the club.
New signings Ben Davies, Malik Tillman, Rabbi Matondo, Tom Lawrence, Antonio Colak and John Souttar have already strengthened Giovanni van Bronckhorst’s squad ahead of the 2022/23 campaign.