The first Prince of Cieszyn and founder of one of the two oldest Piast lines in Silesia, the eldest son of the Prince of Opole, Władysław, and his wife, Eufemia, the daughter of Władysław Odonic. The name of his wife is unknown but they had three children; two sons, Władysław and Kazimierz and a daughter, Wiola Elżbieta.
      Since his father, Władysław, had three other sons in addition to Mieszko (Bolko, Kazimierz and Przemko), Mieszko received one of the four provinces of the former unified Duchy of Opole after his father's death around 1281. Initially he was due to become the Prince of Racibórz, but finally gained the throne of Cieszyn, while the youngest of the brothers, Przemko, became the Prince of Racibórz.
      In revenge for Henryk IV Probus' (Henry IV the Righteous; one of the pretenders to the throne of Cracow and the Polish crown) sending his wife – Mieszko and his brothers' sister – back to her family, and partially fearing political centralisation, Mieszko backed the Bishop of Wrocław, Tomasz II, sheltering him in Racibórz. Owing to similar apprehensions about centralisation he withheld support for two other Piasts who were pretending to the throne. These were the Prince of Wielkopolska, Przemysław II and the Prince of Gniewkowo and later King of Poland, Władysław Łokietek. In this respect he behaved in a similar way to other Polish Piasts. Their fears were motivated by the insufficiently developed nature of liege homage in the subdivided Poland of that time. This gave rise among the provincial princes to fears of losing their duchies. An alliance with another pretender to the Polish throne, the King of Bohemia, Vaclav II, would give Mieszko the assurance that he would retain his property. Mieszko entered the alliance with Vaclav II de facto against Łokietek on 17 January 1291. Mieszko granted Vaclav the right to enter his strongholds and guaranteed him freedom to take his armies through the Duchy of Cieszyn, in return for which Vaclav promised to pay a ransom if ever Mieszko should be taken into captivity and to support him in conflicts with other princes.
      After Przemysław Wielkopolski, another pretender to the Polish crown, had given up Cracow and the rank of prince of Cracow on 10 April 1291 and 11 August 1292 Prince Mieszko swore allegiance to King Vaclav II. He then supported Vaclav in his attempts to gain the Polish crown. Mieszko took part in Vaclav's campaign against Łokietek in 1292, during which he participated in the march on Cracow and in the battle of Siewierz. He also took part in the coronation of Vaclav II as King of Poland in Gniezno in 1300. In return for this support the king's son, Vaclav III, married Mieszko's daughter, Wiola, who took the name of Elżbieta on marriage.
      The policy of entering into alliances with the kings of Bohemia continued after the death of Vaclav II in 1305, with Mieszko backing his son Vaclav III, the new King of Bohemia and Poland.
      In domestic affairs Mieszko proved to be a shrewd ruler. He carried out intensive colonisation, tripling the number of settlements in the Cieszyn Castellany. He contributed to the growth of towns, conferring various degrees of municipal rights on Cieszyn, Oświęcim, Zator, Bielsko, Skoczów and Frysztat.
      Before his death he divided the Duchy of Cieszyn into two; the Cieszyn part which Kazimierz received and the Oświęcim part which was given to Władysław.