After the armistice that ended World War I in November 1918, Dowbor-Muśnicki helped organize a new Polish army around the disbanded 1st Corps and its officers. On January 6, 1919 he was nominated by the Supreme People's Council, the temporary ruling body of the province of Greater Poland, as the new commanding officer of all the Polish forces in the area. Two days later he arrived to Poznań and on January 16 he officially assumed his post, replacing Major Stanisław Taczak during the Greater Poland Uprising against Germany in the disputed region.