An organotin-substituted Dawson-type phosphotungstate was covalently linked to a trithiocarbonate group by postfunctionalization methods. This organopolyoxometalate led to a series of polyoxometalate (POM)–poly(N,N-diethylacrylamide) hybrids in a controlled way through reversible addition–fragmentation chain transfer (RAFT) polymerization. Detailed comparison with and without the presence of POMs revealed that they do not profoundly disturb the RAFT mechanism, despite their oxidative power. The molar masses of the polymers were in the range of 10 to 100 kg mol−1 and molar mass dispersities of the composites were low (Mw/Mn<1.5). The POM building block in the hybrids retained the photocatalytic reactivity of the parent Dawson polyanion [P2W18O62]6−. Smaller, more homogeneous, and colloidally more stable silver nanoparticles were formed with the covalently linked POM–polymer compound than with its single unbound components.