The swivel jack assembly is used with trailers to vertically position a trailer tongue for mounting onto a hitch of the towing vehicle. The swivel jack assembly includes a jack-mounting bracket welded to an outer housing of the jack, and a tongue-mounting bracket mounted onto the tongue portion of a trailer. The jack also includes a novel swivel mechanism for pivoting the mechanism in either an upright support position or a horizontal stowed position. A cup-shaped section of the jack-mounting bracket nests within a cup-shaped section of the tongue-mounting bracket. When in the upright position, the jack extends vertically and may be used to raise or lower the tongue and support the trailer. The swivel jack assembly keeps the trailer in a level position when the trailer is disengaged from the towing vehicle. The swivel jack assembly is pivotally mounted onto the trailer tongue such that they can be pivotally repositioned to a stowed position when not in use.