This paper discusses the normativity of the principle of harmony with nature, starting from the historical engagement of the United Nations with the ecological agenda from 1968 to the issuance of Resolution 64/196 in 2009, on Harmony with Nature. The harmony with nature is analyzed as a pre-legal principle in the natural laws that govern ecosystems. The normativity of the principle of harmony with nature is discussed through the theoretical lenses of Josef Esser and Friedrich Müller, thus proposing harmony with nature as a general principle of law, which emerges within the scope of international environmental law considering the jurisprudence of various courts around the world. Its normative structure is also demonstrated, identifying ecological balance in its normative core. Finally, the implicit provision of the principle of harmony with nature in the Constitution of Brazil, from 1988, is discussed. To support the character of the legal principle of the ethical narrative of harmony with nature, from the historical movement of evolution of the rights of non-human living beings, this work draws on the thoughts of Alfred von Verdross, Klaus Bosselmann, Cançado Trindade, Robert Kolb, Vladmir Oliveira da Silveira, Maria Mendez Rocasolano, Alexandre Kiss, and Dinah Shelton.