The 1st Battalion sailed on the Kildonan Castle, and arrived at the Cape about 22nd November 1899.
The battalion was sent out among the corps troops, and during December and January was employed in the central district of Cape Colony.
Along with the 1st Yorkshire and 1st Essex the Welsh Regiment was put into the 18th Brigade under Major General T E Stephenson, the 2nd Warwick joining later. The 18th Brigade took the place of the 12th in the VIth Division, and bore a most distinguished part in the events which turned the tide of fortune. The work of the VIth Division is sketched under the East Kent Regiment, and that of the brigade under the Yorkshire Regiment. That the Welsh Regiment performed their share of the task in a manner worthy of all praise is proved by the following quotation from the despatch of Lieutenant General Kelly-Kenny of 20th February, relating to the attack on Cronje at Paardeberg: "I will take an opportunity of bringing to notice the special acts of devotion to duty on the part of individuals; I confine myself at present to representing the fine spirit and gallantry of all the troops engaged; I feel bound, however, to bring to your lordship's notice now the very gallant conduct of the 1st Battalion Welsh Regiment, who were on our right flank: a portion of the battalion charged right up to the Boer laager with the bayonet in the finest possible manner, losing heavily in their gallant attempt to capture it". The Welsh have to thank some pertinacious catechists in the House of Commons for the publication of this despatch: the object of the catechists was not, however, to add to the glory of this or any other regiment.
At Paardeberg the Welsh had 1 officer killed and 5 wounded, 15 men killed and 57 wounded.
On 6th March at Poplars Grove, or Osfontein, the Welsh were again engaged; and on the 10th at Driefontein, or Abraham's Kraal, they had a post of honour. In his telegraphic despatch of 11th March Lord Roberts says, "The brunt of the fight fell on Kelly-Kenny's division, two battalions of which—the Welsh and the Essex—turned the Boers out of two strong positions at the point of the bayonet". Various correspondents referred in terms of highest praise to the work of the Welsh. The Press Association correspondent, in an admirable account wired from the field, after referring several times to the way in which the battalion advanced in face of a heavy fire,—both gun and rifle,— said, "Just before dusk the Welsh Regiment gallantly rushed the position at the point of the bayonet, taking a kopje and clearing a considerable portion of the ridge. The scene was witnessed by Lord Roberts through a telescope". The battalion lost Captain Lomax, Lieutenant Wimberley, and 29 men killed, 5 officers and over 100 men wounded.
Six officers and 4 non-commissioned officers and men were mentioned in Lord Roberts' despatch of 31st March 1900.
The battalion was engaged at Leeuwkop, south-east of Bloemfontein, on 22nd April, when they lost Captain Prothero and 1 man killed, and 1 officer and 7 men wounded.
In the advance from Bloemfontein to Pretoria, and thence to the Koomati Valley, the battalion was in the engagements outside Johannesburg and Pretoria, and in the battles at Diamond Hill and Belfast, but had no serious losses. They were stationed at Godwaan from 4th September till 12th October, and were then sent to Barberton, where they remained till 22nd November, when they were sent to occupy various stations in the Koomati Valley—Krokodile Poort, Nelspruit, Alkmaar, Elandshoek, and Godwaan. While stationed in this most unhealthy district the battalion was decimated by fever. In May 1901 the battalion was taken to Johannesburg, remaining there as part of the garrison till March 1902, when they were sent to hold a line of blockhouses from Horn's Nek to Hekpoort west of Pretoria, and they were on this duty when peace was declared.
The battalion furnished a maxim gun detachment with the 1st Mounted Infantry under Colonel Alderson, and a company of Mounted Infantry in Colonel De Lisle's battalion.
In Lord Roberts' final despatch 12 officers and 20 non-commissioned officers and men were mentioned.
In a train incident at Alkmaar on 20th May 1901 a lieutenant, a non-commissioned officer, and a private gained mention for great gallantry; and in Lord Kitchener's final despatch 4 officers and 4 non-commissioned officers were mentioned.