We describe a polymeric ionic liquid (PIL) derived from trimethyl(p-vinylbenzyl)ammonium chloride ([VBTAm]Cl) that efficiently catalyzes the N-formylation of amines employing CO2 and PhSiH3 at room temperature with low catalyst loadings in near-quantitative yield. Under more forcing conditions N-methylated products can be selectively obtained. The PIL catalyst can be easily recovered and reused repeatedly without a decrease in activity. The reaction mechanism was studied in situ using high-pressure NMR spectroscopy and a tentative mechanistic cycle has been proposed.