The 4th contingent, 392 strong, all ranks, under the command of Lieutenant Colonel A Aytoun, Captain in the Argyll and Sutherland Highlanders, sailed from Brisbane upon 18th May 1900, on the Manchester Port. The ship touched at Beira and also at Port Elizabeth, but the contingent landed at Cape Town, and was taken to the north of the Orange River Colony. There they joined the mounted column of Colonel Hickman, which, after assisting to keep De Wet off the railway, was ordered to Pretoria, where it joined General Ian Hamilton's Division, and took part in the march to and occupation of Balmoral on the Delagoa railway. During this march the 4th QIB was transferred to Colonel Pilcher's mounted corps, Mahon being in command of all Ian Hamilton's mounted men. During the month of August Ian Hamilton's force marched to Rustenburg and back to Pretoria. On 31st August Captain Jones' company started with Mahon for the Eastern Transvaal, and with that leader took part in General French's memorable march to Barberton (see Imperial Light Horse). The headquarters of the 4th QIB joined Brigadier General Ridley's mounted column, which, in conjunction with a force under General Clements, operated in the Central Transvaal. On 15th October the regiment moved into Pretoria, and on the 18th left to reinforce General Plumer, who was working to the north of the capital. They were now again in the corps of Colonel Hickman.
In his telegram of 22nd October 1900 Lord Roberts said: "Paget reports a successful surprise made by a small force under Lieutenant Colonel Lloyd, West Riding Regiment, and another by the Queensland Imperial Bushmen, under Lieutenant Colonel Aytoun (Argyll and Sutherland Highlanders), west of the Pienaars River. We had one casualty, Trooper Brickwood, Queensland MI, severely wounded. Eighteen Boers were captured, and large numbers of sheep and cattle were taken". And in his telegram of 24th October Lord Roberts said: "On the 24th Colonel Aytoun, Queensland MI, with a small force, captured two field cornets, Doonsen and De Beer, and 5 waggons. One man of Colonel Aytoun's was wounded". Again, on 12th November, Lord Roberts wired: "Paget reports that a patrol of Queensland Bushmen, under Lieutenants Bell and Kemp, captured six of the enemy near Pienaars River yesterday,—two of the six are badly wounded".
Apart from these instances in which the Queenslanders were specially mentioned, the various Bushmen contingents under Baden-Powell, Paget, and Plumer had endless fighting during August, September, October, and November, and were very successful in making large captures from the enemy in the district north of Pretoria. While in this district the 4th had 4 men killed, and Lieutenant J Higson (who afterwards died of his wounds) and 3 men wounded.
On 29th November Paget and Plumer fought a stiffly contested battle at Rhenoster Kop, north of the Delagoa Railway. The enemy were in great force, and strongly posted. The engagement has been referred to under the New Zealand Mounted Rifles. The 4th Queenslanders were said to have done well. They suffered several casualties. Lieutenant Colonel Aytoun having been sent to hospital on 20th November, Major W Deacon took over the command.
The regiment, along with the greater part of Plumer's mounted men, was, in the beginning of February 1901, railed from the Transvaal to Naauwpoort in Cape Colony, and took part in the arduous but most exciting work which the pursuit of De Wet through and out of that colony entailed (see 3rd Queensland Mounted Infantry Contingent and 4th Victorian Contingent). Lieutenant Kellaway was wounded at Grasfontein on 2nd February, and the corps had several other casualties. Plumer's men got much credit for the fine way they held on to their elusive opponent. The regiment was afterwards with General Plumer in the north of the Transvaal, and in the great sweep to the Piet Retief district.
The bulk of the contingent under Major Deacon sailed for home on 7th July 1901.