The wedding took place at Villa D'este in Como, with guests reportedly including George Clooney and his girlfriend Elisabetta Canalis.
A representative for Krasinski told Us Weekly: "John and Emily were married on Saturday in a private ceremony."
A source added: "It was an outdoor ceremony and absolutely beautiful. It was an official ceremony. They are husband and wife."
The pair are said to have been staying at Clooney's Lake Como estate since the July 4 weekend.