Thea Ekström grew up in Söndrum, Halmstad. In 1937, she moved to Stockholm to study music and pursue a career as an organist, all according to her father's wishes. Before she began her studies in painting in the early 1950s, she devoted much time to working in music, both as a pianist and a choir singer. What she experienced during these years would later inspire several of her paintings, and music occasionally makes its presence felt in her works through depicted instruments.

During the 1950s, Ekström studied at ABF and the Pernby School of Painting in Stockholm. As a free student, she also had the opportunity to attend the Royal Academy of Fine Arts' life drawing classes and Oscar Reutersvärd's art history lectures. Initially, Ekström painted more realistically, later transitioning to a freer style of painting with a cohesive colour palette. Despite the differences in her painting methods, distinctive signs and symbols recur, unifying her visual world over time.

In 1960, Ekström achieved her major breakthrough with a solo exhibition at the Lilla Paviljongen gallery in Stockholm. The Moderna Museet acquired the work Poplars for its collection. The following year, in 1961, she gained international attention when she participated in a group exhibition at Galerie Cordier in Paris, followed by a solo exhibition in 1962. Throughout the 1960s, Ekström also exhibited in several locations in the USA, thus establishing an international career.