A soybean cultivar designated 3421683 is disclosed. Embodiments include the seeds of soybean 3421683, the plants of soybean 3421683, to plant parts of soybean 3421683, and methods for producing a soybean plant produced by crossing soybean 3421683 with itself or with another soybean variety. Embodiments include methods for producing a soybean plant containing in its genetic material one or more genes or transgenes and the transgenic soybean plants and plant parts produced by those methods. Embodiments also relate to soybean cultivars, breeding cultivars, plant parts, and cells derived from soybean 3421683, methods for producing other soybean cultivars, lines or plant parts derived from soybean 3421683, and the soybean plants, varieties, and their parts derived from use of those methods. Embodiments further include hybrid soybean seeds, plants, and plant parts produced by crossing 3421683 with another soybean cultivar.