Department of Peacebuilding Act of 2021 This bill establishes a Department of Peacebuilding in the executive branch, dedicated to peacebuilding, peacemaking, and the study and promotion of conditions conducive to both domestic and international peace and a culture of peace. The mission of the department includes the cultivation of peace and peacebuilding as a strategic national policy objective and development of policies that promote national and international conflict prevention, nonviolent intervention, mediation, peaceful conflict resolution, and structured conflict mediation. The department shall collaborate with others to promote personal and community security and peace by supporting policies to address personal and family violence, including suicide; reduce drug and alcohol abuse; and create, through local community initiatives, peace projects that facilitate conflict resolution and healing of societal wounds. A Federal Interagency Committee on Peace is established to coordinate the actions of the department with other federal agencies. The Department of Defense and the Department of State must consult with the department concerning nonviolent means of conflict resolution when a conflict between the United States and any other government or entity is foreseeable, imminent, or occurring. The department shall encourage citizens to observe and celebrate the blessings of peace and endeavor to create peace on Peace Days.