He was born in 1904 in Lamia. From a young age, he became a student of religious icon painter, Y. Sarafianos, and even presented a solo exhibition at a café in Lamia (1923). He studied at the Athens School of Fine Arts with Iakovidis, Geraniotis, Mathiopoulos and Lytras (1923-1929). At the same time, he earned his living, by creating illustrations. He continued his studies in Paris, with P. Le Doux and H. Morisset (1930-1932). He briefly returned to Greece, and presented his first official solo exhibition (Hermes gallery, 1932), he was associated with the leftist circles of the organization Young Pioneers and co-founded the art group Free Artists in 1934. In 1935, he returned to Paris, where he attended painting classes at the Ecole des Beaux Arts and at the Colarossi and Grande Chaumière independent art academies, up until 1939, when he settled permanently in Athens.
During the Occupation, he joined the Greek Resistance and in 1944, he participated in initiatives for the establishment of the Greek Chamber of Fine Arts. Around this time his attitude towards modern art was skeptical, negative almost, and his painting maintained a realistic orientation, leaning towards social criticism. In 1941, he was appointed museum artist at the National Archaeological Museum, where he worked until 1969.
Circa 1947 he attempted a change of direction towards abstract painting, which he strongly defended in the following years, with his work and his writings. In 1949, he became head of the art group Oi Akraioi, which contributed to the spread of abstract forms in Greece. Though his relation to abstract painting was never exclusive or permanent, it was associated with his historic role, as an artist and intellectual, in the modernization of Greek art.
He published the texts of his lectures and essays on art: Today's painting (1951), Eulogy of Silence (1970), Memento: creating Art - Aesthetic essays (1971) and Intellectual Responsibility (1973).
His work was presented in solo and group exhibitions in Greece and abroad. He participated in the Biennales of Sao Paulo (1953, 1955-silver medal, and 1957), Alexandria (1959) and Venice (1960). In 1973, he declined the 1st National Award, protesting against the dictatorship (1967-74).
One year after his death (Athens, 1975), a retrospective exhibition of his work was organized at the Athens National Art Gallery (1976), with more to follow in Greece and abroad.
His house was donated to the Municipality of Agia Paraskevi by his wife and, since 1999, it operates as the Alekos Kondopoulos Municipal Library and Museum, while in the Lamia Municipal Gallery Alekos Kondopoulos, there is a permanent exhibition of his representative works.