As a younger son, Christian had little prospect of inheriting the Electorate of Saxony, and instead received from his father in 1650 the administration of the former Bishopric of Merseburg, which had been confiscated after the Reformation.

In a testament signed on 20 July 1652, the Elector John George I settled on an official division of the Albertine lands.

According to the will of John George I, Christian received Merseburg and the cities of Bad Lauchstädt, Schkeuditz, Lützen, and Zwenkauand with their castles, half of the towns of Brehna, Zörbig, and Finsterwalde, and the Margraviate of Lower Lusatia, including the towns and castles of Lübben, Dobrilugk, Finsterwalde, Guben, Luckau, Calau, and Spremberg; this settlement created the Duchy of Saxe-Merseburg with Christian as its ruler.

On 25 November 1659, Christian gave Count Erdmann Leopold of Promnitz his approval to permit some Protestant refugees from Silesia, mainly from the duchies of Sagan and Glogau, to live quietly in Neudorf.

Christian's older brother, John George II, found himself frustrated by his late father's will, since it divided the lands of the Electorate contrary to the principle of primogeniture.