Neergaard's greatest challenges as a politician were as prime minister and finance minister after the Easter Crisis of 1920, organizing the return of South Jutland to Danish rule and having to deal with the economic crisis brought on by World War I.[2] He also had a significant influence on the content of the Constitution of 1915.[2]
Neergaard's largest work as a historian, Under junigrundloven (1892-1916), is still considered the primary work on Danish politics 1848–1866.[2] In addition to his political activities and work as a historian he also dealt with journalism, and in 1884 he founded a cultural and literary magazine, Tilskueren.[3]