Preparation of antibody drug conjugates (ADCs), an emerging novel class of highly targeted biological hybrid agents, necessitates precise control of conjugation reactivity. Antibodies have complex multistranded architectures, and specific modification of natural antibodies has proven quite challenging. Here, we demonstrate that cooperative activity of a multimetallic metallopeptide enables efficient site-specific antibody functionalization, based on molecular recognition of the constant Fc region. This interplay of multiple metal centers enables introduction of an orthogonal alkyne handle into monoclonal or polydonal antibodies from different species in an Fc-specific fashion. Elaboration of this simple functionalization allows preparation of conjugates with fluorophore, affinity handle, and pharmacological agents. This method opens a new opportunity for quick and easy production of well-defined antibody conjugates from a variety of antibody sequence and species of origin.