During the liberation of France, Zyromski joined the National Front resistance movement. Following the SFIO congress to sign the Unity Charter proposed by the PCF, he joined the PCF. He obtained his first electoral mandate in 1946 as Councilor of the Republic for the Lot-et-Garrone department, which he would keep for two years, not running for reelection in 1948. Within the PCF, Zyromski showed a surprisingly tolerated independence even when, in 1959, he signed a tribune in which he criticized the lack of internal democracy within the party. Following the 1968 invasion of Czechoslovakia, however, he stopped all activities within the party. Following the death of his wife in 1962, he moved to Melun where he died in 1975.