Marcinkevičius was born in 1930 in Važatkiemis, Prienai district. In 1954 he graduated from Vilnius University History and Philology faculty with a degree in Lithuanian language and Literature. He worked for a number of years as vice-chairman of the board of the official Union of Lithuanian Writers.
Having grown up during the post-war period, Marcinkevičius evokes in his poetry a romanticized version of childhood spent in the Lithuanian countryside, of first love, of man's relationship with nature. In his poetry specific and solid peasant thinking is combined with a mind seeking to draw broad general conclusions, and the tradition of Lithuanian poetry singing the earth's praises with contemporary modes of poetic thought. As a poet, he has sought to grasp the essence of national experience and give it fresh artistic expression. In his lyrical verse Marcinkevičius strives to comprehend the real meaning of what is going on inside man and society and moves the reader with his ardent lyrical confessions.
For most his life Justinas Marcinkevičius lived and wrote during the complex times of Soviet totalitarianism. He defended the cultural self-awareness of his nation. The poet brought back humanistic idea in describing a man, continued on the romantic and lyric poetry tradition, valued the aesthetic side of literature, as opposed to the heroic and propagandistic style of socialist realism. Marcinkevičius wrote and continues to write poems in a romantic and modern style. Justinas Marcinkevičius is regarded as one of the most prominent members of Sąjūdis.
After the emergence of Marcinkevičius' first book I Plead for a Word in 1955, he has published fourteen collections of poetry, three historical plays, two collections of essays, a novella and various translations into Lithuanian.