He was one of the so-called népi ("from the people") writers, named so because they aimed to show – propelled by strong sociological interest and left-wing convictions – the disadvantageous conditions of their native land.

From 1918 to 1919 he took part in various left-wing students and youth workers' movements, being present at an attack on Romanian forces in Szolnok during the Hungarian Republic of Councils.

On 22 December 1920 his first poem was published (El ne essél, testvér) anonymously in the Social Democrat daily Népszava.

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.

Illyés worked for the Phoenix Insurance company from 1927 to 1936, and after its bankruptcy he became press referent to the Hungarian National Bank on French agricultural matters (1937 – 1944).

His first critical writing appeared in November 1927 in the review Nyugat ("Occident") – the most distinguished literary magazine of the time –which from 1928 regularly featured his articles and poems.

Subsequently, he was invited to the editorial board of Nyugat and became a close friend of its editor, the post-symbolist poet and writer Mihály Babits.

Having been refused by the authorities to use the name Nyugat for the magazine, he continued to publish the review under a different title: Magyar Csillag ("Hungarian Star").

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.