We give an accurate historical and scientific account of a practically unknown manuscript written by Ettore Majorana in French. The retrieved text deals with Quantum Electrodynamics by using the formalism of field quantization, and it is here reported, for the first time, in English translation. It is likely related to an invited talk for a conference at Leningrad in 1933 which, however, Majorana never attended. Probably this manuscript is one of the last missing papers of the “Senatore folder,” given by (...) Majorana to one student of his at the University of Naples in 1938, just before his disappearance. (shrink)