[3][2] With the help of socialist activist Christian Rakovsky, allegedly a relative,[5] he joined the Social Democratic Party of Romania (PSD) in September 1913, taking part in its activities and collaborating with its press.

[12] Although, like Cristescu, he was criticized by the Comintern for his allegedly minimalist outlook,[13] he rose to the leadership of the PCR soon after the party was outlawed in 1924, and was known at the time under various pseudonyms (including Popescu, Draganov, and Dragu).

[2] After many party activists, including the entire Politburo, took refuge to the Soviet Union, Stefanov stood as leader of the local Secretariat (together with Pavel Tcacenko).

[15] Sentenced in absentia to 10 years of prison in 1925, he was only apprehended in August 1926, after a Siguranța Statului crackdown,[16][2] Stefanov was among those exposed after authorities pressured one of his comrades to hand out the names of all PCR leaders.

[17] Supported by the International Red Aid with interventions from Marcel Pauker (the French lawyer, Maurice Juncker, solicited, was forbidden to appear before the court by the Romanian authorities and expelled from Romania,[18] he was nonetheless sentenced to 8 years for treason during a trial he faced in Cluj (the other person indicted, Vasile Luca, was acquitted)[5] Stefanov served his sentence in Jilava, Văcărești, Doftana, Brașov and Aiud, and was set free in August 1933.

[20] Subsequently, Stefanov engaged in a campaign against alleged Trotskyists, mirroring Soviet measures that led to the Great Purge; a committed Stalinist, he accused both Elena Filipescu and Marcel Pauker of having sided with Leon Trotsky.

[5] During World War II, his son, Asen Draganov [ru], died while fighting the Germans as part of Dmitry Medvedev's partisan detachment.

[2] Stefanov returned to Bulgaria in 1945, being elected in the country's National Assembly and serving as plenipotentiary of the Bulgarian Communist Party's Central Committee in the region of Dobruja.

In 1961 he was denounced during a Plenum of the Central Committee of the PCR, which accused him of having been "divorced from the working class", of having introduced the theory of "neo-serfdom" (see Constantin Dobrogeanu-Gherea), as well as of having advocated a "liquidationist" policy of a united front with bourgeois parties in 1927.

[23] During the later part of his life, Stefanov collaborated with several Bulgarian newspapers and magazines, and also participated in friendship committees seeking to strengthen Bulgaria's relation with Romania, the Soviet Union, and Yugoslavia.