Banér entered the army in 1615, and quickly rose through the ranks, serving with distinction in Sweden's wars against Poland and Russia. Banér was present at several critical battles during the Thirty Years' War, including at the Battle of Breitenfeld and the Battle of Alte Veste. He continued the war even after Gustavus's death, with varying degrees of success.
He died in 1641.
Johan Banér commanded the cavalry of the Swedish right flank at the Battle of Breitenfeld. From here, he successfully repelled several offenses by Gottfried Pappenheim, before finally breaking it altogether. Despite his clear desire to give chase, Banér listened to Gustavus Adolphus's order to return to the line.
In 1633, Banér was sent to the Upper Palatinate (Oberpfalz) to deter Bavarian incursions into the area and to deter the Bavarians from sending troops to aid either or the League of Ostend. In March of 1634, he determined to take the city of Ingolstadt, partly because he was annoyed that Bavaria had a garrison north of the Danube, but mostly because he was frustrated with what amounted to garrison duty.
Johan Banér died on February 26, 1636, at the Battle of Ostra. The volley gun company that killed him did not realize he was there, and he was not recognized until one of his adjutants, who had survived unhurt, identified him.