6 January 1851) – 29 July 1919) was a Russian revolutionary who was one of the founders of the Circle of Tchaikovsky, Land and Liberty and the Socialist-Revolutionary Party.

He graduated from the Kaunas men's grammar school in 1868, studied in St Petersburg at the Medical and Surgical Academy (1868–71) and then at the Institute of Agriculture (1871).

In the same year, he began work on the unification of the Narodnik circles into a single revolutionary organization, which in 1878 was called "Land and Liberty."

Narodnaya Volya favoured agitation among urban workers and intellectuals, rather than spreading propaganda among the peasants (a tactic adopted by the other offshoot of 'Land and Liberty', the 'Black Repartition' group).

When a shipyard was organised for the construction of a ferry crossing on Lake Baikal, the Corps of Ship Engineers needed an experienced and honest accountant, and Natanson took the job.

[3] Historian Shmuel Galai has argued that "for the first time in the annals of Russian parties, it declared organized public opinion to be the main weapon in the struggle against autocracy," in contradistinction to peasant revolt, general strike, or terror.

[4] However, the People's Rights Party proved to be a short-lived venture, as in 1894, Natanson was arrested again and banished to eastern Siberia for ten years.

[3] Natanson remained an active revolutionary even in Siberian exile, maintaining the party treasury and coordinating various organisational tasks.

The successful assassination of the Minister of the Interior Vyacheslav von Plehve, Natanson began to support the terrorist tactics of the Socialist Revolutionaries.

The tactical position adopted by the SRs represented a compromise between the rural agitation favoured by South Russian and Ukrainian populists, the factory organisation favoured by the People's Rights Party and the terrorist tactics embraced by the remnants of 'The People's Will' and some of the revolutionary groups of Moscow and Petrograd.

In September 1904, together with Viktor Chernov and Yevno Azef, he negotiated with Plekhanov, Ulyanov and other social democrats in order to convince them to take part in the common cause.

[3] After the February Revolution broke out, Natanson returned to Russia through German territory "in a sealed wagon", as did Lenin.

[10][11] He became one of the most prominent leaders of the left wing of the SRs, which became increasingly disenchanted with the Provisional Government and with Alexander Kerensky and sharply criticised the defensive position of the SR central committee.

[11] In July 1919, Mark Natanson died in Switzerland from complications of thromboembolism and purulent pneumonia after a surgical operation for a prostate tumor.