We provide the first large‐scale empirical evidence of banks functioning as tax planning intermediaries. We posit that some banks specialize in assisting corporate clients with tax planning. In this role, banks make use of their centrality in financial relationships; access to private information; and ability to structure, execute, and participate in tax planning transactions for clients. We measure bank‐client relationships using loan contracts and measure client tax planning using either the cash effective tax rate or the unrecognized tax benefit balance. Using a difference‐in‐differences design, we find that firms experience meaningful tax reductions when they begin a relationship with a bank whose existing clients engage in above‐median tax planning. The effects of pairing with such tax intermediary banks are concentrated in relationships with larger or longer maturity loans, clients with foreign income or greater credit risk, and when the bank is an industry specialist or has above‐median investment banking activities. Finally, we find that potential clients are more likely to choose tax intermediary banks than nontax intermediary banks, suggesting that tax intermediary banks benefit by attracting new business. Collectively, our results suggest that some banks act as tax planning intermediaries, a role beyond the traditional one of financial intermediary.