Christian's campaign plan for 1626 consisted of three parts; while he led the main army against Tilly, Ernst von Mansfeld would attack Wallenstein, supported by Christian of Brunswick. In the event, Mansfeld was defeated at the Battle of Dessau Bridge in April, while Christian of Brunswick's attack failed completely and he died of disease in June.

Outmanoeuvred and hampered by torrential rain, Christian turned back to his base at Wolfenbüttel but decided to stand and fight at Lutter on 27 August. An unauthorised attack by his right wing led to a general advance which was repulsed with heavy loss and by late afternoon, Christian's troops were in full retreat. A series of charges by the Danish cavalry enabled him to escape but at the cost of at least 30% of his army, all the artillery and most of the baggage train. Many of his German allies abandoned him and although the war continued until the Treaty of Lübeck in June 1629, defeat at Lutter effectively ended Christian's hopes of expanding his German possessions.