Thermally stable diamond bonded materials and compacts include a diamond body having a thermally stable region and a PCD region, and a substrate integrally joined to the body. The thermally stable region has a microstructure comprising a plurality of diamond grains bonded together by a reaction with a reactant material. The PCD region extends from the thermally stable region and has a microstructure of bonded together diamond grains and a metal solvent catalyst disposed interstitially between the bonded diamond grains. The compact is formed by subjecting the diamond grains, reactant material, and metal solvent catalyst to a first temperature and pressure condition to form the thermally stable region, and then to a second higher temperature condition to both form the PCD region and bond the body to a desired substrate.