Irradiation of platinum(II) bis(beta-diketonates) in the presence of hydrosilanes and olefins results in olefin hydrosilation. The initial rate of hydrosilation is dependent upon the choice of beta-diketonate ligand, hydrosilane, and olefin. Formation of an active catalyst requires the presence of either triethylsilane or triethylvinylsilane during a brief period of irradiation. Addition of the second reactant results in hydrosilation without further irradiation. Substantial inhibition of hydrosilation is observed when dibenzo[a,e]cyclooctatetraene is added following irradiation and prior to addition of the second reactant, but not when mercury is added following irradiation, These results indicate that the active form of the photogenerated catalyst is homogeneous rather than heterogeneous. Correlation of hydrosilation reactivity with the spectroscopic changes which occur during irradiation suggests that the primary photoproduct is not catalytically active and that a secondary photochemical reaction results in the loss of one of the two beta-diketonate ligands and the formation of the active catalyst.