Zinchenko, 31, leaves Arsenal three-and-a-half years after arriving from Manchester City in a £30 million deal. Since 2022, Zinchenko made 91 appearances for Arsenal, scoring three goals along the way.
The 75-time Ukrainian international spent the last six months on loan at Nottingham Forest, where Zinchenko made just five Premier League appearances.
In Amsterdam, Zinchenko has put pen to paper under a six-month contract that will allow technical director Jordi Cruyff, who starts his job on February 1st, to assess the left-back's value and the club's finances again in the summer.
In a club statement, director of football Marijn Beuker welcomed Zinchenko and praised his experience as a valuable asset.
"With Oleksandr, we are bringing in an experienced player who gives us an immediate quality boost in the pursuit of Champions League football. As a left-back, he is tactically strong, provides defensive stability and fits perfectly with our way of playing," Beuker said.
"Oleksandr has proven in the Premier League that, in addition to his defensive qualities, he can also play an important role in build-up play and breaking lines. We are therefore very pleased that he will strengthen our squad at least until the summer."
The Eredivisie is no new ground for Zinchenko, who spent the 2016-17 season on loan at PSV, where he played 17 games across all competitions.
Ajax are currently in fourth in the Eredivisie, trailing second-placed Feyenoord by one point and leaders PSV by 18 points.