The construction of the NDL Main Building had been delayed since the establishment of the organization, but the discussion progressed based on the Act on the Construction Committee for the National Diet Library (Act No. 6 of 1948), which was promulgated along with the National Diet Library Act; thus it was decided that the Main Building should be built on the site of the former Embassy of Germany (Nagata-cho, Chiyoda Ward, Tokyo Prefecture) located directly north of the Diet Building.
組織の発足より建設が遅れていた国立国会図書館の本館庁舎は、国立国会図書館法と同時に公布された国立国会図書館建築委員会法（昭和23年法律第6号）に基づいて検討が進められ、国会議事堂の北隣にあった旧ドイツ大使館跡地（東京都千代田区永田町）に建設されることになった。