In August, the 1st Division moved south to the Somme sector to participate in the Battle of Amiens and later the attack on the Hindenburg Line. Through his "careful preliminary preparations and sound tactical knowledge", Mackay contributed to the successes of his brigade and was once more mentioned in despatches. For his service as a brigade commander, he was appointed a Companion of the Order of St Michael and St George (CMG) in the 1919 New Year Honours. He was also awarded the French Croix de guerre for his service on the Western Front.