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Although widely used in catalysis, the multistep syntheses and high loadings typically employed are limiting broader implementation of highly active tailor-made arylborane Lewis acids and Lewis pairs. Attempts at developing recyclable systems have thus far met with limited success, as general and versatile platforms are yet to be developed. We demonstrate a novel approach that is based on the excellent control and functional group tolerance of ring-opening metathesis polymerization (ROMP). The ROMP of highly Lewis acidic borane-functionalized phenylnorbornenes afforded both a soluble linear copolymer and a cross-linked organogel. The polymers proved highly efficient as recyclable catalysts in the reductive N-alkylation of arylamines under mild conditions and at exceptionally low catalyst loadings. The modular design presented herein can be readily adapted to other finely tuned triarylboranes, enabling wide applications of ROMP-borane polymers as well-defined supported organocatalysts.