The proclamation of the Second Republic opened the road to Prados’ committment with the society of his time. The altruism of the writer led him to embrace the cause of the poor and the disadvantaged. He collaborated in the journal Octubre, and after 1934 his support for the left parties became more explicit, as his unfinished works Calendario incompleto del pan y el pescado and Llanto de octubre showed.
He revealed the complexities of his inner world in his passionate books
(La voz cautiva, Andando, andando por el mundo, and La tierra que no alienta) that recovered the deep romanticism of his writing, much influenced by Mayakovsky and the contemporary art of the Soviet Union.

As a response to the way in which a sector of his old friends closed ranks around what will soon be known as the Generation of '27, Prados decided (together with Aleixandre and Cernuda, who later changed their minds) to stay out of the anthology that Gerardo Diego published in 1932 who, nevertheless, included him against his will.

In the period immediately before the war, he supported the work of the youth group that published the journal Sur, and became very close to the political stand taken by Alberti and Neruda, and to publications coming from the USSR. The poetic series Seis estancias revealed the crisis, both ideological and sentimental, which overwhelmed the writer. When war broke out, alarmed by the uncontrollable climate of violence that reigned in Malaga, Prados moved to Madrid and became a member of the Alliance of Anti-fascist Intellectuals.

He worked on humanitarian missions sponsored by the Republic, helped to organize the II International Congress of Writers, and supervised the edition of several books (Homenaje al poeta Federico García Lorca, and Romancero general de la guerra de España).
He also published his El llanto subterráneo and Llanto en la sangre. Romances (1933-1936). In 1938, he received the National Prize for Literature for Destino fiel, (a collection of his poetry on the war) and donated the money to the Republican government. His friendship with Antonio Machado that started during the war is evidenced in the text that Machado dedicated to him by those dates.

He moved to Barcelona where he and Altolaguirre took charge of the publications of the Ministry of Education. He joined the editorial board of Hora de España and met María Zambrano, a writer who will remain a close friend.

The printing press that Altolaguirre installed in the ruins of the Monastery of Gualter published Prados’ Cancionero menor para los combatientes, a book of intense lyricism that collected his poems about the war. He fell into a deep depression that made him throw the manuscript of the diary that he had written during the war into the sea. Prados crossed the Spanish border into France with Antonio Machado, carrying with him only a pocket Bible and a copy of Gerardo Diego’s Antología.