The 22-year-old arrived at Ibrox from Leicester City two years ago in return for a training compensation payment. He now departs for the biggest transfer fee Rangers have ever received in their 150-year history.
Ajax are set to pay an initial £18.7million for the defender, with the move potentially rising to £22.7million with add-ons. What's more, Rangers have also agreed a 10% sell-on clause.
The Dutch giants have already spent big this summer after splashing over £26million on Tottenham's Steven Bergwijn and over £8.5million on AZ Alkmaar defender, Owen Wijndal.
A statement on the Dutch outfit's official website said: "Ajax has reached an agreement with Rangers and Calvin Bassey for the transfer of the defender to Amsterdam.
"The English-Nigerian player has signed a contract with Ajax that will take effect immediately and will run for five seasons, until June 30, 2027."
Since arriving in Glasgow, Bassey has made 65 appearances for the Gers across all competitions.
The player helped the team to a Scottish Premiership crown in 2020/21 and a Scottish Cup win in 2021/22.
Bassey was also part of the team which reached the Europa League final last season - one which ended in a defeat to Eintracht Frankfurt.
In spite of the loss, the player was named in the Europa League Team of the Season.
A statement on the Glasgow club's official website said: "Rangers 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.
"Bassey played his part in Rangers' historic 55th league title victory, won the 2022 Scottish Cup, while also having a huge role in the incredible Europa League run to the final in Seville last season.
"We wish Calvin all the best for his future career."