Mieszko was the son of Bolesław III Wrymouth, Duke of Poland, and Salome von Berg-Schelklingen, daughter of Duke Henry of Berg (of Wuerttemberg). Mieszko was Bolesław's fifth son, and the ducal couple's fourth.
Mieszko's children were:
In accordance with the testament of Poland's Duke Bolesław III Wrymouth, Poland was divided into 4-5 hereditary provinces distributed among his sons, with the royal province of Kraków being reserved for the eldest son, who was to be High Duke of all Poland.
One of the provinces, Greater Poland, was granted to Bolesław's third-oldest son, Mieszko (and was subsequently divided among Mieszko's descendants and successors). In 1173 Mieszko was promoted to the throne of Kraków and became High Duke of Poland (Latin: dux maximus, dux totius Poloniae); but he was soon expelled from Kraków by his younger brother, Casimir II, and from Greater Poland by his son. Mieszko III never abdicated his rights or ambitions, and returned to Kraków four times before he died in 1202.