[2] Christian was born in 1599 at the Gröningen Priory near Halberstadt (in today's Saxony-Anhalt), the third son of Duke Henry Julius of Brunswick-Lüneburg (1564–1613) with his second wife Elizabeth (1573–1626), daughter of the late King Frederick II of Denmark.

In 1621, Christian was one of the few men to continue rallying behind Frederick V, who had only the year before claimed and been deposed from the throne of Bohemia following his crushing loss at the Battle of White Mountain.

The newly united Protestant army moved into Alsace, leaving Heidelberg, the capital of the Palatinate, to fall to Count von Tilly in September 1622, effectively forcing Frederick V out of the war.

After intense foraging and ravaging of the Alsace region, Christian and Mansfeld moved north in Lorraine, and upon the news of the Spanish siege of Bergen op Zoom, they marched to the relief of the city, fighting the Battle of Fleurus (29 August 1622) and in the midst of the battle, Christian displayed his well-known courage and stubbornness on the field by leading four unsuccessful cavalry charges against the Spanish lines under Fernández de Córdoba.

[3] The Battle of Fleurus was claimed as a victory by both sides: although the Protestant commanders fled headlong with their cavalry, abandoning their infantry, baggage and artillery on the field, so by any measure losing the battle itself, their surviving cavalry's ability to make it through to the Dutch Republic did in some measure contribute to the relieving of the Protestant stronghold of Bergen op Zoom, providing grounds to claim the encounter as a strategic victory — although modern historians regard it as having made little difference in that regard.

He was outrun and outmaneuvered 10 miles short of the Dutch border, and in a stand typical of Christian's bravery, he was nonetheless decisively defeated at the Battle of Stadtlohn on 6 August 1623, when he lost all but 2,000 of this 15,000-man army.

Three days after Stadtlohn, Frederick V signed an armistice with Ferdinand II, ending the former's resistance to what seemed as impending Catholic domination of the Holy Roman Empire.