Due to her father's work in the navy, she spent some of her early years in Weihai, China, where Mercia learned Mandarin Chinese.
[4] She grew up in Ditchling and later was educated at Westonbirt School, Gloucestershire and St Anne's College, Oxford University where she read Russian Literature.
In 1948, she graduated with an MA degree from Oxford and visited Bulgaria to participate in the international youth brigade building the Koprinka Reservoir.
As a foreign udarnik, Mercia was invited along with other international participants to meet Georgi Dimitrov in the Euxinograd palace on the Bulgarian Black Sea Coast.
Returning to the United Kingdom in 1948, MacDermott enrolled in a Bulgarian language course at the University of London's School of Slavonic and East European Studies.
MacDermott subsequently lectured on the Bulgarian national liberation movement in the region of Macedonia at Sofia University's Faculty of History.