A Universal Single Person Undermount Fixture Installation Device is sued for the installation of undermount style plumbing fixtures by a single installer. This device includes a support that is set atop the counter/substrate and spans the opening where the fixture is to be raised into its final position. This support includes an attachment that protrudes down through the opening and engages the fixture through the drain opening to allow it to be raised from above the countertop. This device also includes a method for final tightening of the fixture from above while in full view of its current alignment to the opening within the counter/substrate. The tool can be disengaged to release from the fixture drain opening once the fixture is fastened in accordance with the manufacturer's instructions.