Bonello was born on the 11th June 1936. He completed his studies at the Royal University of Malta from where he graduated LP (1954) and LL.D. (1958).
He served as judge of the European Court of Human Rights in Strasbourg. He has specialized in human rights and has contributed extensively to the development of the law protecting human rights in the island.
Bonello is also an authority on Maltese history and history of art. He is also a postal history expert and the owner of a huge collection of antique Maltese postcards. He co-authored with Graham Smeed Maltese Picture Postcards, 1898-1906 (1985) and several other publications.
Bonello is Cavaliere della Republica, an honour bestowed upon him by the Italian President, and Knight of Magisterial Grace of the Sovereign Military Order of St. John. Bonello is also a committee member of Fondazzjoni Patrimonju Malti.