Although Smilets is credited with being descended "from the noblest family of the Bulgarians", his antecedents are completely unknown.
Judging by the landholdings of Smilets’ brothers Radoslav and Vojsil, the family held extensive lands between the Balkan Mountains and Sredna Gora.
Apart from the information that Smilets became emperor of Bulgaria according to the wishes of Nogai Khan, we know nothing of the circumstances of Smilec's accession.
Joachim was executed for treason in 1300 by emperor Theodore Svetoslav, George I's son, and historian John Van Antwerp Fine Jr. theorizes that the alleged treachery might be linked to the obscure period when Smilets overthrew George Terter I.
In fact, in spite of the usually pro-Byzantine policy of Nogai, Smilets was quickly involved in an unsuccessful war against the Byzantine Empire at the beginning of his reign.