A conversion seat for a marine vessel that converts from a lean post configuration to a seat configuration. In a stowed position, the seat is stored vertically exposing a cushion that can be used as a lean post. When a positive lock is released the seat is able to rotate, in some embodiments with an assist from a gas strut, two-hundred and seventy (270) degrees until the seat lands on a horizontal surface. When released, a backrest opens to a desired angle providing a comfortable seat or sun pad. To stow the seat for use as a lean post, the backrest is folded back down and then the seat is able to rotate back through the two-hundred and seventy (270) degrees to its vertical stowed position.