A facile approach for the preparation of mesoporous polymer nanospheres (MPN) and mesoporous carbon nanospheres (MCN) with complete shape retention based on surface-confined atom transfer radical polymerization of various methacrylate monomers from in situ generated initiator-modified hard silica nanospheres template is developed. This approach yields mesoporous silica-polymer hybrid nanospheres (MSPN) with mesopores that are uniformly filled with covalently attached well-defined poly(methacrylate)s. The silica frameworks are subsequently etched, resulting in MPN. Pyrolysis of MSPN and subsequent removal of silica template resulted in the production of MCN. They retain the size, shape, and mesoporous ordering of the silica template nanospheres. Gel permeation chromatography analysis of the silica free polymers reveals that they have controlled molecular weights and low polydispersities (PDIs). Kinetics studies reveal that the molecular weight of the grafted polymer increases linearly with time, maintaining low PDIs, indicating the living nature of the polymerization. The mesoporous polymer material is found to have low dielectric constant, which paves the way for their use as low-dielectric constant materials in microelectronics. This approach allows fabrication of functional MPN using functional comonomers, which are successfully used for the synthesis of “clickable” mesoporous polymer nanospheres, removal of ionic contaminates through anion exchange, and glucose sensing.