The division was part of XXIII Reserve Corps and was recruited primarily in the Prussian provinces of Pomerania and West Prussia, but the 212th Reserve Infantry Regiment was a Hanseatic regiment, raised in Hamburg and Bremen.
The 45th Reserve Division fought on the Western Front, entering the line in October along the Yser and remaining there until April 1915, when it went into the fight for Ypres.
Thereafter, the division went into the trenchline around Verdun, remaining there until the end of September 1917, when it joined the Battle of Passchendaele.
In 1918, it fought in the German spring offensive, including the breakthrough at St. Quentin and the follow-on battles in the Montdidier-Noyon region.
Over the course of the war, other changes took place, including the formation of artillery and signals commands and a pioneer battalion.