At the UN-level, it has only recently been acknowledged that the welfare of animals is not, but should be, part of the sustainable development agenda. With the outbreak of the COVID-19 pandemic, the interconnections between animal welfare and protection on the one hand, and on the other hand, ecosystem destruction, species extinction, the climate crisis, industrial animal agriculture and the emergence of zoonoses, have come to the fore. Arguments have also been made that sustainability and animal protection is something of an oxymoron with, in particular, farm animals being treated as vehicles to achieve sustainability rather than being agents who under a justice perspective should be beneficiaries of the sustainability transition. To address the un/sustainabilities in the nexus of animals and sustainability, critical theory perspectives draw out pathways for transformation. Critical Sustainability Studies is being formulated. Critical Animal Studies is already well established. Both converge in what could develop into a new field, Interspecies Sustainability Studies. Moreover, we are observing the birth of another new field, the Veterinary Humanities, with indications of a Critical Veterinary Humanities emerging. In this paper, it is discussed what critical theory perspectives bring to the intersection of animals and global sustainability. In conclusion, it is suggested that interspecies sustainability needs to be conceptualised as a critical theory to address the multiple sustainability crises and to protect animals, end their exploitation and facilitate their flourishing.