A marine pipeline installation system is provided for laying a pipeline and/or installing a subsea riser. The system includes a pipeline guide supported at an elevated position by the tower for guiding the pipeline from a first trajectory extending between the reel and the pipeline guide to the firing line along said tower. The pipeline guide is supported by the tower via an associated guide support frame, the support frame being adapted to allow for displacement of the pipeline guide between a pipelaying position, wherein one end of the pipeline guide is positioned in the firing line, and a retracted, non-operable position. The guide support frame allows movement of the pipeline guide in a combined upward direction and direction towards the reel, such that in the retracted position of the guide support frame the length of the first trajectory is essentially the same as in the pipelaying position.