The UDA West Belfast Brigade is the section of the Ulster loyalist paramilitary group, the Ulster Defence Association (UDA), based in the western quarter of Belfast, in the Greater Shankill area. Initially a battalion, the West Belfast Brigade emerged from the local "defence associations" active in the Shankill at the beginning of the Troubles and became the first section to be officially designated as a separate entity within the wider UDA structure. During the 1970s and 1980s the West Belfast Brigade was involved in a series of killings as well as establishing a significant presence as an outlet for racketeering.

The brigade reached the apex of its notoriety during the 1990s when Johnny Adair emerged as its leading figure. Under Adair's direction the West Belfast Brigade in general and its sub-unit "C Company" in particular became associated with a killing spree in the neighbouring Catholic nationalist districts of West Belfast. With Adair and his supporters suspicious of the developing Northern Ireland peace process and the Combined Loyalist Military Command ceasefire of 1994, the West Belfast Brigade increasingly came to operate as a rogue group within the UDA, feuding with rival loyalists in the Ulster Volunteer Force before splitting from the UDA altogether in late 2002. Ultimately Adair was forced out and the brigade was brought back into the mainstream UDA. It continues to organise, albeit with less significance than in its heyday. Matt Kincaid is the incumbent West Belfast Brigade leader and under his leadership the brigade has again become estranged from the wider UDA.

The origins of the UDA lay in west Belfast with the formation of vigilante groups such as the Shankill Defence Association and the Woodvale Defence Association. The latter, formed by Charles Harding Smith, became the largest of a number of similar groups and was instrumental in the establishment of the UDA in September 1971, having begun military training of its members two months earlier. In 1972, when Jim Anderson was serving as acting chairman of the UDA, a West Belfast battalion was formed as a separate part of the UDA, such was the volume of membership within the area. The battalion was divided into three separate companies: A Company, which was based on the Highfield estate with some members in Glencairn, B Company which covered the Woodvale area, and C Company for the Shankill Road itself. Battalions covering the other three areas of Belfast as well as South East Antrim and North Antrim and Londonderry were formed soon afterwards and before long these were re-designated as brigades after the UDA experienced a rush of members.

The battalion fell under the initial control of Davy Fogel, under whose leadership the group undertook a programme of erecting barricades between the Shankill and the neighbouring republican Falls and Springfield Roads. However, the local strongman was Harding Smith, who had been held in prison on charges of gun-running in London. When he returned in early 1973 Harding Smith ran Fogel out of the area and became commander of the battalion himself, whilst also becoming joint chairman of the UDA as a whole with Anderson.

Harding Smith soon became embroiled in a feud with East Belfast leader Tommy Herron, whilst also facing a growing rival in his own area in the shape of Andy Tyrie, the commander of A Company. Tyrie was chosen as the overall Chairman of the UDA in 1973, with Anderson off the scene. Tyrie had initially been seen as a compromise candidate between the two real powerhouses of Harding Smith and Herron but before long he began to assert his independence. Herron was killed in late 1973 and soon after Tyrie and Harding Smith became openly hostile after Tyrie sanctioned a trip by UDA activists to Libya. Harding Smith publicly condemned the move, arguing that Libyan leader Muammar Gaddafi was a friend of the Provisional IRA, and in January 1975 he announced the secession of the West Belfast Brigade from the UDA. However, after a power struggle Harding Smith was driven out of Northern Ireland following two failed attempts on his life, according to Peter Taylor by one of Tyrie's men. The West Belfast Brigade immediately returned to the mainstream UDA fold.

The west Belfast area also saw the formation in 1973 of the Ulster Freedom Fighters (UFF) by former Harding Smith ally John White. Modelled on the Red Hand Commando, the UFF was to be an armed elite of killing units to be nominally separate from the legal UDA but actually a flag of convenience under which UDA members could kill Catholics. The model soon spread from west Belfast to the rest of the UDA.

When Harding Smith left Northern Ireland in 1975 Tommy Lyttle was chosen as his replacement as Brigadier, following a brief interlude during which John McClatchey served as leader. Under Lyttle however the West Belfast Brigade entered a period of stagnation and from being the main area of activity it fell way behind the new centres of North and South Belfast. A rare foray into murder by a member of the brigade proved somewhat disastrous during the 1977 Ulster Workers' Council strike. Kenny McClinton stopped a bus as part of a road blockade and entering the vehicle, shot and killed driver Harry Bradshaw, a Protestant. This, along with press revelations that the UDA had written a letter of apology to his widow in which they enclosed a ten-pound note, helped to further undermine the already unpopular strike. During the 1980s James Craig, another former associate of Harding Smith, had been attached to the West Belfast Brigade as "fundraiser-in-chief", a role which saw the brigade move increasingly towards racketeering. Craig particularly favoured protection rackets that targeted Belfast's building firms and gained a lot of money through these, both for the brigade and for himself. Arrested in 1985 for racketeering, the case collapsed and he returned to the Shankill but was soon asked to leave because of his personal enrichment and he left to link up the John McMichael's South Belfast Brigade instead. According to Billy McQuiston, a member of the West Belfast Brigade, the activities of the brigade during the 1980s helped to make the UDA unpopular on the Shankill as they were identified with gangsterism.

Despite this the West Belfast Brigade saw an influx of new young members in the 1980s and before long Lyttle came under pressure to give them something to do. Lyttle shared Craig's predilection for gangsterism but was less interested in murder and so turned to his intelligence officer Brian Nelson who drew up a list of leading republican targets and October 1987 Nelson dispatched a group of raw recruits to the nationalist Ballymurphy area to kill the first of these, a 66-year-old taxi driver by the name of Francisco Notorantonio. Despite appearing on the list Notorantonio had only ever been very loosely connected to the Irish Republican Army and Sinn Féin and had ended his active associations with republicanism several years earlier. In fact Nelson, who was the highest-ranking British intelligence agent in the UDA, had seized on Notorantonio at the last minute after being informed by his handlers that his initial first target was actually a high-ranking British agent in the Provisional Irish Republican Army known as "Stakeknife" (believed to be Freddie Scappaticci). "Stakeknife" was seen as much too important to be killed and so a last minute switch was made. Nonetheless, the killings continued, with C Company becoming the most active, under the command of William "Winkie" Dodds. They struck again, based on Nelson's list, on 10 May 1988 with the murder of Terence McDaid. This murder however was an error as the actual target had been his older brother Declan, whose striking physical resemblance to Terence meant that C Company had received the wrong photograph from Nelson. Nelson also provided details on Gerard Slane, who was killed by B Company on 22 September 1988. Slane was shot dead at his Falls Road home with the UDA claiming he was a member of the Irish People's Liberation Organisation. The most notorious killing was that of solicitor Pat Finucane in February 1989, carried out by brigade member Ken Barrett using information provided by RUC Special Branch.