Mašin was the son of immigrants originally from Cerhenice in the Kingdom of Bohemia, who had settled in the Principality of Serbia in 1846, during the reign of Prince Alexander Karađorđević.

[1] His father, Jovan Mašin [sr], was a skilled physician who worked at the Prince's court and always kept loyalty to the Karađorđević dynasty.

[1] Despite this and thanks to his intelligence, Mašin received protection, as a young officer, from King Milan I, from the rival Obrenović dynasty.

28–29 May] 1903, according to plans finalized two days earlier by the conspirators, Mašin spent the afternoon at the Officers' Club in Belgrade.

[8] At four in the morning he led the group of officers who received the Russian representative, who requested the removal of the bodies of the couple from the palace garden (present-day Pioneers Park).

[14] In May 1906 the Serbian government was willing to comply with British demands and Mašin, among other military personnel, retired, which allowed the resumption of diplomatic relations between Serbia and the United Kingdom on the third anniversary of the May Coup 11 June [O.S.