E. Rossoni and B. Zuanella agree that the surname derives from the name Petrus, through dialectal forms with the suffix -at.

E. Rossoni specifies that it is an almost unique surname, derived from an alteration of Petrus, first transformed into Perus and then, with the pejorative suffix -at, into Perat.

B. Zuanella proposes instead an origin linked to the locality of Pèrati, a district of the parish of Luico/Livek (Slovenia), where the surname is endemic. There stands the late-medieval little church of San Pietro/Svet Peter with the cemetery of the whole parish, and the devotion to Saint Peter favoured the birth of the surname Pérat in the nearby village. It arose with the Romance suffix -at from the hagionym Petrus, specifically from the dialectal form Pero (Pero + at = Pérat). He mentions as an analogous formation the family name (hišno ime) Peteràdi at San Pietro al Natisone, which gave rise to the surname of the Slovenian poet Don Pietro Podrecca, whose ancestor was called Peteràt.

B. Zuanella documents the surname in the parish of Luico/Livek as early as the 17th century: in 1612 (fil. Pauli Pèrat de Luico), in 1638 (Andreas Peratt de Luicho, baptismal books of San Leonardo) and in 1649 (Philippus Perat de Liuak, baptismal books of San Pietro). He also records the form Pérato or Pérat at Azzida from the beginning of the 17th century: 1612 (Zuan Perato), 1644 (Andrea Perato) and 1680 (Agnes uxor Matthiae Perat). He further documents the marriage celebrated on 9 November 1676 at San Leonardo between Luca Perat of Luico and Marina, daughter of Jacobi Bucauaz of Sverinaz, and the family’s later move to Brizza near Savogna, where the house endured until after 1800.