The manuscripts were stolen in the 1930s.
Police also recovered drawings and letters between Verga and the poet Gabriele D'Annunzio, philosopher Benedetto Croce and dramatist Luigi Pirandello.
The documents were lost when Verga's son, Giovanni Verga Patriarca, lent them to a historian in the small town of Barcellona Pozzo di Gotto in Sicily who then refused to return them and hid them.
"The precious documents were never returned and attempts to retrieve them have always failed as they were very well squirrelled away," Antonio Coppola, who led the police operation, told AFP.
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In 1975, Verga's grandchild won exclusive rights to the missing manuscripts and agreed to sell them to the Sicilian city of Catania where the author was born should the documents ever resurface.
Police on the case caught a break when manuscripts by Verga appeared on an auction list at Christie's in Milan.
A raid on a house in Rome belonging to the historian's daughter, referred to by police only by the initials A P, produced the documents.
Verga, who died aged 81 in 1922, was part of the Italian realist movement.
"The House by the Medlar Tree", inspired director Luchino Visconti's 1948 film "The Earth Trembles".