Blackburn went on leave in France from 29 April to 7 May. The 10th Battalion entered the fighting on the Western Front in June, initially in a quiet sector of the front line. While in this area, Blackburn was selected as a member of a special raiding party led by Captain Bill McCann. In the early hours of 23 July, the 10th Battalion was committed to its first significant action on the Western Front during the Battle of Pozières. Initially, A Company under McCann were sent forward to assist the 9th Battalion, which was involved in a bomb (hand grenade) fight over the O. G. 1 trench system. Held up by heavy machine gun fire and bombs, McCann, who had been wounded in the head, reported to the commanding officer (CO) of the 9th Battalion, Lieutenant Colonel James Robertson, that more help was needed. About 05:30, a detachment of 50 men from 16 Platoon, D Company, 10th Battalion, was then sent forward under Blackburn to drive the Germans out of a section of trench. Blackburn, finding that A Company had suffered heavy casualties, immediately led his men in rushing a barricade across the trench, breaking it down, and using bombs, they pushed the Germans back. Beyond this point, preceding artillery bombardments had almost obliterated the trench, and forward movement was exposed to heavy machine gun fire.
Blackburn, along with a group of four men, crawled forward to establish the source of the German machine gun fire, but all four of the men were killed, so he returned to his detachment. He went back to Robertson, who arranged support from trench mortars. Under the cover of this fire, Blackburn again went forward with some of his men, but another four were killed by machine gun fire. Another report to Robertson resulted in artillery support, and Blackburn was able to push forward another 30 yards (27 m) before being held up again, this time by German bombers. Under cover from friendly bombers, Blackburn and a sergeant crawled forward to reconnoitre, establishing that the Germans were holding a trench that ran at right angles to the one they were in. Blackburn then led his troops in the clearing of this trench, which was about 120 yards (110 m) long. During this fighting, four more men were killed, including the sergeant, but Blackburn and the remaining men were able to secure the trench and consolidate. Having captured the trench, Blackburn made another attempt to capture the strong point that was the source of the machine gun fire, but lost another five men. He therefore decided to hold the trench, which he did until 14:00, when he was relieved. By this time, forty of the seventy men that had been under his command during the day had been killed or wounded. Sometime that night, Blackburn took over command of D Company, but was relieved the following morning.
For his actions, Blackburn was recommended for the award of the Victoria Cross (VC), the highest award for gallantry in battle that could be awarded to a member of the Australian armed forces at the time. Describing his actions in a letter to a friend, the normally retiring Blackburn said it was, "the biggest bastard of a job I have ever struck". In recommending him for the VC, his commanding officer, Lieutenant Colonel Stanley Price Weir, observed, "Matters looked anything but cheerful for Lieutenant Blackburn and his men, but Blackburn lost neither his heart nor his head".
The 10th Battalion was relieved from its positions at Pozières in the late evening of 25 July, having suffered 327 casualties in three days. Blackburn was temporarily promoted to the rank of captain on 1 August, due to the heavy losses. The battalion spent the next three weeks in rest areas, but returned to the fighting during the Battle of Mouquet Farm on 19–23 August, incurring another 335 casualties, from the 620 that were committed to the fighting. Following this battle, the 10th Battalion went into rest camp in Belgium, and on 8 September, Blackburn reported sick with pleurisy and was evacuated to the 3rd London General Hospital. He relinquished his temporary rank upon evacuation, and was placed on the seconded list.