After the outbreak of the Spanish Civil War he joined the confederal militias, fighting on the Extremadura front.

He came to command the Pío Sopena battalion,[2] which was deployed on the fronts of Talarrubias and Casas de Don Pedro.

[4][3] Towards the end of the war he fled to Alicante,[5] but upon reaching the port he discovered that there were no boats for the refugees.

He was taken prisoner by Franco's forces and imprisoned in the concentration camps of Albatera and Porta Coeli.

Olegario Pachón himself verified the degree of inactivity of the anarchist organization and made it known to the CNT headquarters in exile.