His graduation thesis, published in 1819, on the history of the Merovingian Mayors of the Palace, attracted the attention of the Prussian reformer Baron Stein, by whom he was employed in 1820 to edit the Carolingian chroniclers for the newly founded Historical Society of Germany.

In search of materials for this purpose, Pertz made a prolonged tour through Germany and Italy, and on his return in 1823 Stein entrusted him with publication of the series Monumenta Germaniae Historica, texts of all important historical writers on German affairs before 1500, as well as of laws, imperial and regal archives, and other valuable documents, such as letters, falling within this period.

[2] In 1821 he was made secretary of the archives, and in 1827 principal keeper of the royal library at Hanover; from 1832 to 1837 he edited the Hannoverische Zeitung, and more than once sat as representative in the Hanoverian second chamber.

In 1842 he was chief librarian at the Royal Library in Berlin, where he shortly afterwards was made a privy councillor and a member of the Academy of Sciences.

In connection with the Monumenta Pertz also began the publication of a selection of sources in octavo format, the Scriptores rerum germanicarum in usum scholarum.