The Serie A club announced on Wednesday the 29-year-old defender has put pen to paper on a three-year contract.
A statement from Sampdoria read: “Niklas Moisander will be a blucerchiato player starting from next season.
“Sampdoria and its president Massimo Ferrero are delighted to announce the signing on a three-year deal of the Finnish defender, who remains under contract with AFC Ajax until June 30, 2015.
“We wish him the best of luck for the end of the season with Ajax and with Finland, and we wait for him in Genoa, confident he will be ready and driven to face this new, fascinating adventure in the world’s most beautiful colours.”
Moisander underwent a medical with the Genoa-based outfit last month.
The Finland captain returned to Ajax in 2012 from AZ Alkmaar for a second spell at the club, having previous played three campaigns for the Amsterdam outfit.
Moisander has started in 23 Eredivisie games for Ajax this season and is currently on international duty with Finland preparing for Sunday’s Euro 2016 qualifier against Northern Ireland in Belfast.