Cutting elements include a substrate, a thermally stable polycrystalline table comprising a superhard material secured to the substrate, and a layer of metal interposed between, and attaching the substrate and the thermally stable polycrystalline table. Methods of forming a cutting element include providing a thermally stable polycrystalline table in a mold, providing a layer of metal on the thermally stable polycrystalline table, distributing a mixture of particles comprising a plurality of hard particles and a plurality of particles comprising a matrix material on the layer of metal, and heating the mold while applying pressure to the mixture of particles to cause the mixture of particles to coalesce and form a substrate and at least partially melt the layer of metal to flow and wet the thermally stable polycrystalline table and the substrate to form an attachment therebetween.