Polymer-grafted nanoparticles are effective for designing hybrid materials with optimal component dispersion and enhanced material properties. The olefin chemistry accessible through ring-opening metathesis polymerization (ROMP) presents a route to polymer-grafted nanoparticles that possess unique chain architectures and chemical functionality difficult to achieve with common surface-initiated polymerization methods. Here, we show that surface-initiated ROMP (SI-ROMP) from silica nanoparticles ranging from 25 to 140 nm in diameter result in grafted polymer chains consisting of poly(norbornene) (PNBE), poly(cyclooctadiene) (PCOD), poly(ethylene) (PE), and bottlebrush polymers with poly(ethylene oxide) as the side chains. Furthermore, the brush heights of PNBE and PCOD polymer-grafted nanoparticles are experimentally measured and directly compared to expected scaling laws to present fundamental understanding into the polymer brush growth during SI-ROMP. It is found that polymer brush topology deviates from expectations near the particle surface. By the use of molecular weight and graft density characterization, it is reported that secondary chain transfer favors polymer network formation close to the surface, while linear chain topologies are favored at distances much further from the particle surface. The work presented here details the necessary SI-ROMP reaction conditions for successfully achieving polyolefin grafts with unique topology, chemical functionality, and thermal properties, which will open new avenues for polymer-grafted nanoparticles to be implemented into hybrid materials.