The selective catalytic decomposition of formic acid into hydrogen and carbon dioxide has been achieved in water under mild conditions. For the first time, a ruthenium ion in combination with a series of oligocationic, ammoniomethyl-substituted triarylphosphines was used for this reaction, as opposed to previously used anionic and neutral ligands. These cationic phosphines vary in size and charge and therefore have different hydrophilic, steric, and electronic properties. Excellent catalytic activities were achieved in the formic acid dehydrogenation reaction and correlations between the activity and the ligand structure were made. High turnover frequencies (TOFs) of 1950 h−1 and turnover numbers (TONs) over 10 000 were obtained through optimization of the catalytic system.