Compounds bearing aryl-sulfur and aryl-phosphorus bonds have found numerous applications in drug development, organic materials, polymer science, and homogeneous catalysis. We describe palladium-catalyzed metathesis reactions of both compound classes, each of which proceeds through a reversible arylation manifold. The synthetic power and immediate utility of this approach are demonstrated in several applications that would be challenging to achieve by means of traditional cross-coupling methods. The C(sp²)–S bond metathesis protocol was used in the depolymerization of a commercial thermoplastic polymer and in the late-stage derivatization of a drug. The C(sp²)–P variant led to the convenient preparation of a variety of phosphorus heterocycles, including a potential chiral ligand and fluorescent organic materials, via a ring-closing transformation.