He wrote the first lexicon and systematic grammar of the Maltese language, and he was the first librarian of the Bibliotheca Publica, the precursor of the National Library of Malta.

[1] In 1753, he was appointed quaresimalista of Gozo, the official preacher of Advent and Lenten sermons at the Matrice, which was considered to be a position of privilege.

[2] Throughout his life, De Soldanis wrote a number of works about the Maltese language, which was his main area of interest.

[6] From 1750 to 1762, de Soldanis worked on a second grammar entitled Nuova Scuola della Lingua Punica, but it was never published.

[3] He also wrote a four-volume Maltese-Latin-Italian dictionary entitled Damma tal-Kliem Kartaginis mscerred fel fomm tal Maltin u Ghaucin between 1750 and 1767.

The manuscript served as the basis for further studies on Gozo,[5] but it remained unpublished until 1936, when the Government Press published a translation in Maltese by Giuseppe Farrugia Gioioso.

This book landed him in trouble with Grand Master Manuel Pinto da Fonseca, since in it he attacked the Order of St. John and argued for the rights of the Maltese.

De Soldanis had to go to Rome to defend himself in front of Pope Benedict XIV, but he returned to Malta in 1752 and was forgiven by Pinto.