Random poly(norbornene)-based terpolymers containing azide, ketone and maleimide functionalities along the side-chain were synthesized using ring-opening metathesis polymerization. Subsequent side-chain functionalizations were carried out using three distinct reactions: maleimide–thiol coupling, 1,3-dipolar cycloaddition, and hydrazone formation. All investigated functionalization transformations proceed with high fidelity and absolute selectivity under mild reaction conditions.