This Review aims to highlight key aspects of tetrapyrrole-based antibody-drug conjugates (ADCs) and significant developments in the field since 2010. Many new conjugation methods have been developed and employed in the past decade, and associated with this, there has been a rising interest in theranostic conjugates. We have investigated the physicochemical properties that tetrapyrroles need to possess in order to be viable photosensitizers for conjugation to antibodies. Differences in conjugation strategies are discussed, and structure-activity relationships of tetrapyrrole-antibody conjugates are reported, where available. As the elegance of bioconjugation techniques has increased, it has paved the way for exceptionally phototoxic, yet highly selective, tetrapyrrole-antibody conjugates, with photocytotoxicities in the nanomolar range, to be synthesized and biologically evaluated.