Siegfried was the youngest son of Prince Henry I of Anhalt by his wife Irmgard, daughter of the Ludovingian landgrave Hermann I of Thuringia.

His father had received the Anhalt territory upon the death of Duke Bernhard III of Saxony in 1212 and was raised to the rank of a Prince of the Holy Roman Empire six years later.

In 1247, after the death of the Thuringian landgrave Henry Raspe, younger brother of his mother Irmgard and last male heir of the Ludovinger dynasty, Siegfried interfered in the succeeding War of the Thuringen Succession.

After the death of his father in 1252, in accordance with the family law of the Ascanian dynasty, Siefgried and his elder brothers Henry II and Bernhard divided the Anhalt lands.

On 17 October 1259,[citation needed] Siegfried married Catherine, who is referred to as filia Regis Sweonum ("daughter of the Swedish King") in contemporary German sources.