After the death of her brother Nicolò in 1531, she claimed the island of Paros, against Crusino III Sommaripa and John IV Crispo.
[1] Her rights where acknowledged in 1535 after a trial in Venice, and she ruled jointly with her spouse, Bernado Sagredo.
Cecilia and her spouse abandoned the fortress at Agousa and was besieged in the castle of Kephalos, were her spouse took command of the defense with the aid of a Florentine outlaw and resisted the Ottoman siege for several days.
In the treaty of surrender, Cecilia Venier was deposed from her position and allowed to depart the island for refuge in Venice, while her spouse were held captive by the Ottomans, but was eventually released from captivity.
However, the Ottoman conquest of Paros reportedly led to atrocities committed against the public: as happened to the non-Muslim population in other islands, old men were killed; young men were made galley slaves; little boys were made janissaries; and the women where ordered to dance on the shore so that the conquerors could choose the most attractive for the lieutentants, enslaving around 6000 of the inhabitants of Paros for slavery in the Ottoman Empire.