Poly(norbornene)-based random copolymers possessing either azide, aldehyde, or ketone functionalities on each repeating unit were synthesized using ring-opening metathesis polymerization. The orthogonal functionalization of the resulting copolymers using 1,3-dipolar cycloadditions and hydrazone formations was investigated. While the azide- and aldehyde-containing copolymers were insoluble in organic solvents, the azide- and ketone-functionalized copolymers were fully soluble in common solvents such as CH2Cl2, THF, and DMF and can be quantitatively functionalized with a library of small organic and biological molecules in a stepwise fashion. The orthogonal functionalization of the ketone/azide copolymers was characterized by NMR and IR spectroscopies and gel-permeation chromatography. A one-pot dual functionalization strategy is also presented that allows for the quantitative dual functionalization of copolymers. This one-pot strategy introduced herein for the preparation of multifunctional macromolecules provides a modular platform for potential applications ranging from electronic materials to polymer-mediated drug delivery.