Fabio Lagonissa (1584/85–1659) was an Italian bishop and papal diplomat.

After studying civil and canon law at the University of Naples he went to Rome and was appointed a referendary of the Apostolic Signatura.

On 21 February 1622 he was consecrated archbishop of Conza, but remained active in the papal curia.

He accompanied Francesco Barberini on his unsuccessful mission to Spain in 1625–26.

[2] After the Infanta Isabella's death in 1633 the nunciature fell into abeyance, and in January 1634 Lagonissa returned to Rome.