In the 2014–15 Pro12, Marshall played his highest number of league games for Leinster, making a total of nine appearances, all but two of these coming as a replacement. He also scored his second try for the senior side against Edinburgh. On 19 April 2015 Marshall made his European debut for Leinster, coming off the bench against Toulon in the 2014–15 Rugby Champions Cup semi-final. Marshall left Leinster at the end of the 2014–15 season, having made 20 first team appearances.