Giacomelli was a self-taught photographer. At 13, he left high school, began working as a typesetter and spent his weekends painting. After the horrors of World War II, he turned to the more immediate medium of photography. He wandered the streets and fields of post-war Italy, inspired by the gritty Neo-Realist films of Vittorio De Sica and Roberto Rossellini, and influenced by the renewed Italian photographer Giuseppe Cavalli, and developed a style characterized by bold, stylized compositions and stark contrasts.
Giacomelli's most successful image is entitled Scanno boy. The picture portrays dark and out-of focus women in an almost unreal fairytale atmosphere, walking towards the observer with only one single and central object in focus: a boy walking with his hands in his pockets. In 2013 the name of the boy has been revealed by Simona Guerra: researcher and niece of Mario Giacomelli. His name is Claudio De Cola and on October 19, 1957, he was exiting the Church of Sant'Antonio da Padova like the people around him, after the Mass. Through several researches in the archives and in the town of Scanno she meet the parents of the boy, who is now in his sixties and does not live in Scanno anymore. His recognition, confirmed by himself, was also done by his parents and by his mother Teopista in particular, who produced several other pictures of the boy providing unquestionable evidence that he was the boy portrayed by Giacomelli.
Giacomelli's most successful series are: The landscapes (1954-2000); Scanno (1957); the images call I Pretini (Little Priests) (1961-1963), a poetic transcription of the everyday life of a group of young priests, resulted from documenting Post-War Italian seminaries.
- Alistair Crawford, The Black Is Waiting for the White: Mario Giacomelli Photographs, Contrasto, Milan, 2009
- Simona Guerra, Mario Giacomelli. My whole life, Bruno Mondadori, Milan 2008
- Simona Guerra Parlami di lui [Tell me about him] Mediateca delle Marche, Ancona, 2007.
- Roberto Maggiori, Enzo Cucchi & Bruno Giacomelli: Cose Mai Viste, Photology, Milan, 2006.
- Alistair Crawford, Mario Giacomelli, Phaidon Press, London, 2006.
- Giacinto Di Pietrantonio, Riccardo Lisi, Antonio Ria, Marco Tagliafierro, Michele Robecchi, Enzo Cucchi and Mario Giacomelli, ELR, Losone, 2003.
- Sandro Genovali, Mario Giacomelli: Evoking Shadow, Charta Books, Milan, 2002.
- Germano Celant, Mario Giacomelli, Photology, Milan, 2001 (with texts of photographic series by Simona Guerra).
- Ennery Taramelli, Mario Giacomelli, Nathan, Paris, 1998.
- Enzo Carli, Mario Giacomelli: The Inner form. Photographs 1952-1995, Charta Books, Milan, 1996.
- Ida Gianelli and Antonella Russo, Mario Giacomelli, Castello di Rivoli, Turin, 1992.