Electrodes, modified with [Ru(bpy)2PVP10]n(ClO4)2 metallopolymer:gold nanoparticle composites, are used for the high sensitivity detection of nicotinamide adenine dinucleotide, NADH, using electrochemiluminescence, ECL; bpy is 2,2′-bipyridyl and PVP is poly (4-vinylpyridine). Incorporation of 12.5 nm gold nanoparticles protected with 4-dimethylaminopyridine, DMAP-AuNPs, causes the overall ECL efficiency to decrease with increasing nanoparticle loading. However, the absolute emission intensity and signal-to-noise ratio are both higher for the nanocomposite than for the parent metallopolymer. The ECL intensity depends linearly on [NADH] from 10 fM to 10 μM with a limit of detection, LOD, of 5 fM. The wide dynamic range and low limit of detection make these nanocomposite films attractive for biosensor development.