A marine pipeline installation vessel for laying a pipeline on the seabed, said vessel at least being adapted to carry out the reel lay method, wherein the vessel comprises: • a storage reel for storage of the pipeline to be laid, • a pipeline launch tower mounted to the vessel, which pipeline launch tower is adapted to launch the pipeline in a firing line along said tower; • a pipeline guide which is mounted at an elevated position to the pipeline launch tower, which pipeline guide has pipeline guide surface member providing an essentially circular or semi-circular pipeline guide surface, which pipeline guide is adapted to guide a pipeline from a storage reel over the pipeline guide into the firing line, • a pipeline straightening assembly comprising one or more straightening tracks , used to undo plastic deformation of the pipeline, wherein the pipeline guide comprises a base frame member which supports thereon the pipeline straightening assembly , wherein the base frame member is pivotally connected about an axis to the tower , so that the base frame member is pivotal in a pivot direction (P) about the axis about approximately 90° between • a first position, wherein the base frame member extends vertically and the straightening assembly is aligned with the firing line , and • a second position, wherein the base frame member extends essentially horizontally and the base frame member and the straightening assembly are remote from the firing line , and wherein a displacement drive for the base frame member is provided that comprises one or more drive members , e.g. hydraulic cylinders, that are arranged between the tower and the base frame member to perform the tilting of the base frame member , characterized in that the pipeline guide surface member is supported by a pipeline guide support frame member , e.g. an arm member, that is supported by the base frame member so as to pivot along with the base frame member , wherein the base frame member and the pipeline guide support frame member connected thereto are pivotable in the pivot direction (P) about the axis such that the pipeline straightening assembly is displaceable together with the base frame member about approximately 90°, between the first position thereof with the straightener tracks adjacent the firing line and the second position thereof with the straightener tracks essentially below the pipeline guide surface member in a non-operative location. • a storage reel for storage of the pipeline to be laid, • a pipeline launch tower mounted to the vessel, which pipeline launch tower is adapted to launch the pipeline in a firing line along said tower; • a pipeline guide which is mounted at an elevated position to the pipeline launch tower, which pipeline guide has pipeline guide surface member providing an essentially circular or semi-circular pipeline guide surface, which pipeline guide is adapted to guide a pipeline from a storage reel over the pipeline guide into the firing line, • a pipeline straightening assembly comprising one or more straightening tracks , used to undo plastic deformation of the pipeline, • a first position, wherein the base frame member extends vertically and the straightening assembly is aligned with the firing line , and • a second position, wherein the base frame member extends essentially horizontally and the base frame member and the straightening assembly are remote from the firing line , <EOS>