Arriving in September, the battalion's involvement was limited to mainly defensive operations, and it remained on the peninsula for only a couple of months before the Allied evacuation in December.

Its first significant battle there came at Pozières on 28 July 1916 where the battalion suffered heavily during a night-time attack on the heights, losing 12 officers and 350 other ranks killed or wounded, many of whom were caught in thick wire obstacles that had been left intact by the pre-attack artillery bombardment.

After wintering in Belgium, in early 1918 the 25th Battalion moved south to Somme as the Australian divisions were transferred there to help blunt the German spring offensive in March and April, undertaking a defensive action around Villers-Bretonneux as the Allies fought to defend the vital railhead of Amiens.

[8] In the lull that followed, minor actions were fought around Morlancourt and Hamel, before the Allies launched their Hundred Days Offensive around Amiens in August.

Exhausted by the fighting earlier in the year, its final action came in early October 1918 against the Beaurevoir Line,[1] after which it was disbanded to provide reinforcements to the 26th Battalion with a view to undertaking further operations, but this did not eventuate before the war ended.

[14] Territorial designations were introduced in 1927, at which point the battalion adopted the title of the "Darling Downs Regiment" and the motto Vestigia Nulla Retrorsum.

[16] Following the outbreak of the Second World War, the 25th Battalion undertook periods of continuous training in the greater Brisbane area as part of efforts to improve the nation's readiness.

Initially it undertook defensive duty on the coast around Caloundra, but as the Japanese advanced within the Pacific the 25th was moved north to Townsville in May 1942 and then deployed to New Guinea in July.

For his actions during the fighting around Slater's Knoll, one 25th Battalion member, Corporal Reginald Rattey, received the Victoria Cross.

The honours it inherited at this time were: North Africa; Syria 1941; Merjayun; Chenim and Rharife; Damour; Mazaraat ech Chouf; South-West Pacific 1942–1945; Kokoda Trail; Ioribaiwa; Eora Creek–Templeton's Crossing II; Oivi–Gorari; Buna–Gona; Gona; Lae–Nadzab; Lae Road; Liberation of Australian New Guinea; Ramu Valley; Shaggy Ridge; Borneo 1945; Balikpapan; Milford Highway.