In December of 1939 Polish commander-in-chief Gen. Władysław Sikorski decided that a Polish unit in the French territory of Levant be created. On April 12, 1940 the brigade was officially formed in Syria, with Col Kopański as its commander. The main base of the brigade was established in Homs and the new unit instantly entered the ranks of the French Armée du Levant. As a unit specializing in mountain warfare, the brigade was thought of as a Polish addition to Allied plans for landings in the Balkans. It was modelled after the standard French mountain infantry brigade, with 2 infantry regiments (2 battalions each), artillery regiment, reconnaissance regiment (mounted and motorized), signals, engineers and a staff. Although new recruits arrived on a daily basis (mostly evacuated from Poland through Romania, Hungary, Greece and Yugoslavia), the brigade did not reach the planned numbers of 208 officers and 6840 soldiers and NCO's.
After its capitulation and the annulment of all France's pacts with Poland and the United Kingdom, the commander of the Armée du Levant General Eugène Mittelhauser decided to support the new Vichy government of Philippe Pétain while the Poles were ordered by Sikorski to leave French territory. On June 30, 1940 the brigade defected to Palestine, where it joined the British forces stationed there. Initially composed of 319 officers and 3437 soldiers, it was soon reinforced to roughly 5000 men. Among the distinctive features of the unit was a high morale of the soldiers, all of whom were volunteers. In addition, roughly 25% were well educated, a thing uncommon in European armies of the time.
Based in Latrun, the brigade was equipped with British weapons, reinforced and trained. In October 1940 it was moved to Egypt, where it undertook garrison duties. Among other tasks it guarded POW camps and prepared the fortification of Alexandria. However, as Poland was still formally at peace with Italy, it could not have been sent to the front. On January 12, 1941 the reorganization along the British regulations ended and the unit was renamed to Polish Independent Brigade Group. It was modelled after a British motorized infantry brigade and was then moved to the port of Haifa, whence it was to be transported to Greece. However, before the first of the detachments was embarked on the ships, the Battle of Greece ended as the Germans overran that country.
During the offensive of Erwin Rommel's Afrika Korps, the brigade was finally moved to the front near the fort of Mersa Matruh and then to Sidi Baggush. After a month or so on the front it was again withdrawn to the El Amiriya camp near Alexandria, and on August 18, 1941 the first convoy with brigade's units left for besieged Tobruk. Transported in seven convoys, between August 21 and August 28 the brigade took over the westernmost perimeter of the allied defences and took part in what became known as the Siege of Tobruk. Overnight on December 9, during Eighth Army's Operation Crusader, the Polish brigade seized the strategically-important Madauar Hill, town of Acroma and broke through to the British 8th Army, thus ending the siege. Because of their impact on the battle, the Polish soldiers were awarded with a prestigious title of the Tobruk Rats by their Australian comrades in arms.
On December 13 the Carpathian Uhlan Regiment was detached while the remainder of the brigade was attached to the XIII Corps of the Eighth Army and took part in the attack on the Axis Gazala defensive line on 15 December. Rommel made a fighting withdrawal to defensive positions around El Agheila but a counterattack by him on 21 January, 1942 led to the armies once more facing each other at the Gazala position by early February. On March 17, 1942 the brigade was withdrawn from the front to the El Amiriya camp and then back to Palestine. There it was joined by the Polish forces of General Władysław Anders evacuated from the USSR and was reformed into the 3rd Carpathian Rifle Division. The brigade officially ceased to exist on May 3, 1942.
Throughout its existence it lost 156 killed in action (including 127 in the Siege of Tobruk), 15 missing in action and 467 wounded.