She was the daughter of Prince Vratko Nemanjić, who as a great-grandson of Vukan Nemanjić, Grand Prince of Serbia ), was part of a collateral, elder branch of the Nemanjić dynasty. Her husband was Prince Lazar Hrebeljanović. She was the fourth cousin once removed of Emperor Dušan of Serbia. After the death of her husband at the Battle of Kosovo in 1389, Milica ruled Serbia until 1393 when her son, Stefan Lazarević Hrebeljanović, came of age to take the throne. At that time, much wisdom and personal courage was needed to reign in a country which was nominally free but always under threat of invading forces, from the East and the West. It was difficult to maintain a national spirit without provoking neighbouring kingdoms or pashaluks to raid or plunder. Milica proved herself an able ruler of the country at a very trying time. Her personal tragedy did not interfere with her carrying out her duties. She founded the Ljubostinja monastery around 1390 and later took monastic vows at her monastery and became the nun Eugenia around 1393.
In 1397 she issued the "A Mother's Prayer" together with her sons at the Dečani monastery. She commissioned the repairing of the bronze horos of Dečani. In later diplomatic negotiations with Sultan Bayezid I, Eugenia and Euphemia, the former Vasilissa of Serres, both travelled to the Sultan's court in 1398/99. In 1403, Eugenia went to the Sultan at Serres, arguing in favour of her son Stefan Lazarević in a complicated dispute that had emerged between her two sons and Branković. She was buried in Ljubostinja, her monastery. She was canonized by the Serbian Orthodox Church. Princess Milica was also a writer. She wrote several prayers and religious poems. It appears that her grief and loneliness were captured in her highly lyrical and poetic address to Prince Lazar. Although conceived as a church hymn, it contains a personal note and lyrical tones unusual for solemn and somber church hymnody.
Several streets throughout Central Serbia are named after the Princess. In the once thriving industrial city of Trstenik, Serbia, the main street that runs directly through city center is named Kneginje Milice. Trstenik, Serbia, is the closest major city to her burial site at Ljubostinja Monastery. There is a Kneginje Milice street also located in Lazarevac, in borough Lukavica. The street is about 250 m long. Near that street is Kolubarski trg and Zivojina Zujovica street.
