[3] He was born in Lwów (Lviv) in the Polish–Lithuanian Commonwealth (today part of Ukraine) and was the son of a painter Jerzy Szymonowicz and Teodozja née Korunka.

[2] Shortly after his return to Poland in 1684 he was ennobled by the king and took the name Eleuter (Greek for free, independent).

In 1701, he was adopted by the impoverished Siemiginowski noble family (he paid them a substantial sum for the privilege) and since that time he used their name.

[2] Siemiginowski-Eleuter was the chief artist responsible for the decoration of the interior of the Wilanów Palace near Warsaw.

[5] He painted classicised portraits of members of the royal family and made engravings, including in collaboration with Charles de La Haye.

[6] Siemiginowski established his own school of painting in Wilanów and was a renowned architect (co-designer of the Town Hall in Żółkiew (Zhovkva) among others).