We synthesized three coumarin-substituted benzimidazolium chlorides and their silver(I), ruthenium(II) and palladium(II) N-heterocyclic carbene (NHC) complexes. All compounds were characterized using appropriate spectroscopic techniques and elemental analyses. Single-crystal X-ray structure of a Pd(II)-NHC complex (6b) was also determined. The inhibitory properties of all compounds were tested on the activity of human paraoxonase 1 (PON1). All complexes exhibited weaker inhibitory properties than their corresponding benzimidazolium salts except for complex 6b which is the most active inhibitor with an IC50 value of 3.01 mu M among the compounds reported in this study. A kinetic evaluation showed that this complex inhibits PON1 activity in a non-competitive manner. Molecular docking studies were also performed for 6b in order to obtain more insight into the binding mode.