Ottavio Piccolomini (11 November 1599 – 11 August 1656) was an Italian nobleman whose military career included service as a Spanish general and then as a field marshal of the Holy Roman Empire.
Piccolomini was born in Florence and received a military education as a young boy. He became a tercio pikeman for the Kingdom of Spain at the age of sixteen.
1618 saw the outbreak of the Thirty Years' War. Piccolomini was appointed captain of a cavalry regiment in Bohemia, sent by the Grand Duke of Tuscany to the emperor's army. He fought with distinction under Count Charles Bucquoy at the Battle of White Mountain in 1620 and later in Hungary.
In 1624 he served for a short time again in the Spanish army and then as lieutenant-colonel of Gottfried Heinrich Graf zu Pappenheim's cuirassier regiment in the war with the Milanese. In 1627 he returned to the Imperial service as colonel and captain of the personal guard of Albrecht von Wallenstein, Duke of Friedland. In this capacity Piccolomini fell into disgrace for attempting to extort money from people of Stargard in Pomerania. But his dedication and contrition saw him returned to the rank of "Colonel of horse and foot".