Having grown up in Brasov, in Transylvania, Elena Voinescu studied architecture at the Ion Mincu Institute between 1939 and 1945, receiving her degree the following year (and marrying the same year). Upon graduation, Voinescu returned to Brasov, where she joined the Regional Construction Trust. In 1955, Voinescu moved to Bucharest, receiving a position at the Bucharest Project Institute, where she would remain until her retirement 27 years later. At Bucharest Project, Voinescu was a project architect in a workshop that was invariably led by male colleagues: Tiberiu Ricci, George Mularidis, and finally Paul Focșa.

Among her projects are the Drama Theater in Brasov (1948; Voinescu was the winner of an open competition); pavilion projects for Bucharest zoo; Organ Transplantation Ward of the Fundeni Hospital in Bucharest (with Henrieta Delavrancea, 1959), multiple residential buildings and urban master plans for Bucharest, which she designed between the 1960s and the 1980s. Her most famous work was the extension of the building of the Ion Mincu Institute of Architecture (1970), which included workshops, offices, gym, cafeteria, and an exhibition hall (with Gh. Filipeanu and Al. Beldiman).