Electron transfer (ET) from donor to acceptor is often mediated by nuclear-electronic (vibronic) interactions in molecular bridges. Using an ultrafast electronic-vibrationalvibrational pulse-sequence, we demonstrate how the outcome of light-induced ET can be radically altered by mode-specific infrared (IR) excitation of vibrations that are coupled to the ET pathway. Picosecond narrow-band IR excitation of high-frequency bridge vibrations in an electronically excited covalent trans-acetylide platinum(II) donor-bridge-acceptor system in solution alters both the dynamics and the yields of competing ET pathways, completely switching a charge separation pathway off. These results offer a step toward quantum control of chemical reactivity by IR excitation. We are grateful to M. Newton (Brookhaven National Laboratory), D. Phillips (Imperial College London), A. Orr-Ewing (Univ. of Bristol), D. Clary (Univ. of Oxford), and G. Worth (Univ. of Birmingham) for comments on the manuscript; to I. Rubtsov and R. Schmehl (Tulane University) for discussions; and to the Engineering and Physical Sciences Research Council, Univ. of Sheffield, and Science and Technology Facilities Council for support.