Bladed Gas Turbine Engine (GTE) rotors including deposited transition rings are provided, as are embodiments of methods for manufacturing bladed GTE rotors. In one embodiment, the method includes providing an outer blade ring having an inner circumferential surface defining a central opening, and depositing a deposited transition ring on the inner circumferential surface of the outer blade ring. The outer blade ring can be a full bladed ring or an annular grouping of individually-fabricated bladed pieces. After deposition of the transition ring, a hub disk is inserted into the central opening such that the transition ring extends around an outer circumferential surface of the hub disk. The transition ring is then bonded to the outer circumferential surface of the hub disk utilizing, for example, a hot isostatic pressing technique to join the transition ring and the outer blade ring thereto.