During the German spring offensive of 1918, Operation Michael, Melvill's brigade played key roles in holding and stabilising the lines in the New Zealand sector. Well regarded for his capable leadership, he also led the New Zealand Division from late-June to mid-July 1918 while its nominal commander, Major General Andrew Russell was on sick leave. In the Hundred Days Offensive, his leadership of 1st Infantry Brigade saw it breach the Hindenburg Line and capture the town of Crevecoeur during the Battle of the Canal du Nord on 28 September. For this, and his earlier exploits during the German offensive, he was appointed a Companion of the Order of the Bath in the 1919 King's Birthday Honours. By the end of the war, he had been mentioned in despatches four times. Belgium also recognised his contributions to the war effort; he was appointed as an Officer of the Order of the Crown as well as being awarded the Croix de Guerre.