He was the ninth (fourth surviving) son of John Christian, Duke of Brzeg-Legnica-Wołów-Oława, but the first-born by his second wife Anna Hedwig of Sitzsch.

The marriage of Duke John Christian and Anna Hedwig was considered morganatic and in consequence all the eventual children born of them were excluded from the succession of the Duchy of Legnica-Brzeg.

After the outbreak of the Thirty Years' War, the young August and his family fled to Poland, first to Toruń and later to Ostróda, where his parents died in 1639.

August was raised to the Comital rank with the title of Count of Legnica (German: Graf von Liegnitz) by Bohemian royal order at Regensburg on 12 January 1664.

August, the last male member of the Piast dynasty, died on 14 May 1679 in his castle of Siedminie (Siebenhufen) and 28 September of that year he was buried in the Church of the Holy Trinity in Przeworno.