On 15 August, 1950, following the invasion of South Korea by the Chinese Communist-dominated North Koreans, a Second Battalion of the Regiment was formed as part of the Canadian Army Special Force. On the same date, the serving unit was designated First Battalion. The Second Battalion trained at Sarcee (in Calgary), and Wainwright. On 25 November, 1950 under the command of LCol J.R. Stone, DSO, MC, the battalion sailed from Seattle on the PRIVATE JOE P. MARTINEZ bound for Pusan, Korea.

The Battalion arrived in Korea in December and spent the next eight weeks undergoing training in mountain warfare and small unit tactics. On 6 February, 1951, Second Battalion joined the 27th British Commonwealth Brigade and became the first Canadian Infantry Battalion to be involved in the Korean conflict.

On 22 April, 1951, the Chinese began a major offensive against the UN Forces. Second Battalion, Princess Patricia's Canadian Light Infantry, Third Battalion Royal Australian Regiment and A Company 72nd US Heavy Tank Regiment were tasked to defend the Kapyong Valley. The Chinese attacked in overwhelming force and eventually managed to push the Australians off their position. Second Battalion was then cut off but managed to hold off the Chinese forces and by doing so saved Seoul and countless United Nations lives. In recognition of "outstanding heroism and exceptionally meritorious conduct", a United States Presidential Unit Citation was awarded to Second Battalion, the Australians and the American tank company for their actions at Kapyong on 24/25 April 1951.

On 25 May, 1951, Second Battalion was transferred to the 25th Canadian Infantry Brigade. The Second Battalion was relieved in Korea by the First Battalion in the fall of 1951 and returned to Calgary to take over the airborne role.

On 30 November, 1950, a Third Battalion of the Regiment was formed. This battalion trained in Wainwright, and Camp Borden and Ipperwash, Ontario. It provided reinforcements for both the First and Second Battalions during their tours of duty in Korea.

Third Battalion relieved the First Battalion in Korea in the fall of 1952 and was occupying Hill 355, "Little Gibralter", when the Korean War ended on 27 July, 1953. After twelve months on active service, 3 PPCLI was reduced to nil strength on 8 January, 1954. The Commanding Officer, Regimental Sergeant Major, and selected others transferred to the Second Battalion, Canadian Guards, to form the nucleus of the new unit.