Manhattan Project National Historical Park Act

Manhattan Project National Historical Park Act - Establishes the Manhattan Project National Historical Park as a unit of the National Park System, which may be composed of specified facilities, lands, or interests in one or more eligible areas or parts of such areas in Oak Ridge, Tennessee; Los Alamos, New Mexico; and Hanford, Washington.

Directs the Secretary of the Interior (the Secretary) and the Secretary of Energy (DOE) to enter into an agreement to govern their respective roles in administering the facilities, lands, or interests in land under the DOE's jurisdiction to be included in the Park.

Adds to the Park lands, interests in land, or facilities within the eligible areas which are acquired by the Secretary or are included in an amendment to the agreement.

Requires the Secretary to develop a general management plan for the Park.

Authorizes the Secretary to: (1) provide interpretive tours of historically significant Manhattan Project sites and resources in Tennessee, New Mexico, and Washington state that are located outside the boundary of the Park; and (2) enter into one or more agreements with the head of a federal agency to provide public access to, and management, interpretation, and historic preservation of, historically significant Project resources under the agency's control.