Weir's health had not completely recovered by the time he embarked for Egypt, and he rejoined his battalion on 4 March 1916. After his departure, the 10th had fought through the remainder of the campaign before being withdrawn along with the rest of the Allied force in December 1915. The battalion was subsequently moved back to Egypt. In mid-1916, the bulk of the AIF was transferred to the Western Front, and Weir led the 10th Battalion through July and August 1916 during the Battles of Pozières and Mouquet Farm. At Pozières, the battalion suffered 350 casualties in four days. By the time of the battle, Weir was the only original battalion commander remaining in the 1st Australian Division, and had turned 50 years of age. On 23 August, immediately after Mouquet Farm, Weir was again appointed acting commander of the 3rd Brigade. Exhausted, on 7 September 1916 he asked to be relieved, and his request was granted. He returned to Australia on 23 September 1916, and his AIF appointment was terminated on 14 December. In the Australian official history of the war, Bean observed that despite his age, Weir "took his battalion into the front line, commanded it there throughout its first battle, and remained longer in the field than almost any of the senior militia officers who had left with the original force".