He began studies at the Budapest University's department of languages studying Hungarian and French. Due to illegal political activities he was forced to escape to Vienna in December that year, moving on to Berlin and the Rhineland in 1922. He arrived in Paris in April of that year. He worked numerous jobs including as a bookbinder. For a while he studied at the Sorbonne and published his first articles and translations in 1923. He met the French surrealists, and some of them became friends, among others Paul Éluard, Tristan Tzara, René Crevel.
He returned home in 1926 after an amnesty. His main forums of activity became Dokumentum and Munka, periodicals edited by the avant-garde writer and poet Lajos Kassák.

His first critical writing appeared in the review Nyugat ("Occident") – the most distinguished literary magazine of the time – in November 1927. From 1928 the "Nyugat" regularly features his articles and poems. His first book (Nehéz Föld) was also published by Nyugat in 1928.

Illyés was invited and travelled to the Soviet Union in 1934 to take part in the international writers congress where he met André Malraux and Boris Pasternak. From that year he also participated in the editorial work of the review "Válasz" (Argument), the forum of the young "népi" writers.
He was one of the founding members of the March Front (1937 – 1939), a left-wing and anti-fascist movement. After the Nazi invasion of Hungary in March 1944, Illyés was a fugitive with László Németh as anti-Nazi intellectuals. He became a member of the parliament of Hungary in 1945, and one of the leaders of the left-wing National Peasant Party. He withdrew from public life in 1947 as the Communist takeover of government was approaching. He was a member of the Hungarian Academy of Sciences from 1945 to 1949. He directed and edited the review Válasz from 1946 to 1949

His poetry, prose, theater plays and essays continued to make an important impact on Hungarian public and literary life. On November 2, 1956 he published his famous poem of the Hungarian revolution of 1956, which was not allowed to be republished in Hungary until 1986: "One sentence on tyranny" is a long poem written in 1950.
From the early 1960s he continued to express political, social and moral issues all through his work, but the main themes of his poetry remain love, life and death.