Agnello Participazio (Latin: Agnellus Particiacus) was the tenth traditional and eighth (historical) doge of the Duchy of Venetia from 811 to 827.

He was born to a rich merchant family from Heraclea and was one of the earliest settlers in the Rivoalto group of islands.

[3] The name Agnello appeared in the earliest documents (819 and 820) and in John the Deacon's chronicle Historia Veneticorum.

[8][5] With the attempt of Pepin, the king of Italy and son of the emperor Charlemagne, to invade the Lagoon of Venice, the co-doges Obelerio, Beato, and Valentino degli Antenori fled the duchy of Venetia.

[10][11] Pepin's attempt to invade the duchy of Venetia led the Carolingian and the Byzantine empires to agree the Peace of Aachen in 812, which was ratified in 814.

[12][13] Later, in 820, the young Agnello was sent to Constantinople for the occasion of the coronation of Michael II, the new Byzantine emperor.

[5] The dogeships of Giovanni Galbaio (787–804) and Obelerio degli Antenori (804-811) had been marred by a bitter conflict between a pro-Byzantine faction and a pro-Frankish one, which caused great instability and contributed to Pepin's attempted invasion.

As he was originally form Heraclea, which had been destroyed by his predecessor and by Pepin, he had it rebuilt and renamed Cittanova (New City).

Agnello founded monasteries on the islands of Barnaba and San Giuliano and provided priests with good supplies for the maintenance and decoration of churches wherever this was needed.

[16] The Byzantine emperor Leo V the Armenian sent the relics of St. Zachary, paid for the construction of a monastery and church of San Zaccaria dedicated to this saint and sent architects to build it.