In May 2015, Marshall was named in the Emerging Ireland squad for the 2015 Tbilisi Cup. Ahead of the tournament, Marshall was part of an Ireland XV that took on the Barbarians in Thomond Park. He featured as a replacement for Dan Tuohy, but was on the losing side as Ireland were beaten 22–21. Marshall started the opening game of the Tbilisi against Emerging Italy, came off the bench in the following match with Uruguay and started the final game against hosts Georgia as Ireland won the tournament for the first time.