The recorded history of the Ballymena area dates to the Early Christian period from the 5th to the 7th centuries. Ringforts are found in the townland of Ballykeel and a site known as Camphill Fort in the townland of Ballee may also have been of this type. There are a number of souterrain sites within a 1 1⁄4 miles (2.0 km) radius of the centre of Ballymena.
Two miles (3.2 kilometres) north in the townland of Kirkinriola, the ancient parish church and graveyard possess several indicators of Early Christian settlement, including a souterrain. Also in 1868, a gravedigger found a large stone slab on which was carved a cross with the inscription ord do degen. This refers to Bishop Degen, who lived in Ireland during the 7th century. This stone is now in the porch of St. Patrick's Church (of Ireland) at the end of Castle Street.
At the end of the 5th century, a church was founded in Connor, five miles (8.0 kilometres) south of Ballymena. This was followed by a monastery at Templemoyle, Kells. In 831, however, the Norse invaded the Ballymena area and burned the church.
In the 12th century, the Normans conquered much of County Antrim and County Down after having taken over England the century before. They created the core of the Earldom of Ulster. During this campaign, they built great mounds of earth topped by wooden towers, referred to as mottes, as defensive structures. The Harryville (Ulster-Scots: Herrieville) area's motte-and-bailey is one of the best examples of this type of fortification in Northern Ireland. Some sources , however, credit the Uí Fhloinn with building the mid-Antrim mottes and baileys in imitation of the invaders; the Uí Fhloinn defeated and repelled the Earl of Ulster, John de Courcy, in 1177 and 1178.
In 1315, Edward Bruce (brother of King Robert I of Scotland, known as "Robert Bruce") invaded Ireland. On 10 September 1315, at the Battle of Tawnybrack (five miles (8.0 kilometres) south of Ballymena at Kells), Edward conquered the army of Richard De Burgo, the Norman Earl of Ulster.
In 1576, Queen Elizabeth I granted land, including the town of Ballymena, to Sir Thomas Smith. The lands had been forfeited to the crown after Shane O'Neill's resistance in the 1560s. Smith brought English settlers to the area, among the first pioneers in planting English and Scots settlers in Ireland. By 1581, Smith's settlement failed and the lands reverted to the crown.
On 10 May 1607, King James I granted the native Irish chief, Ruairí Óg MacQuillan the Ballymena Estate. The estate passed through several owners, eventually passing into the possession of William Adair, a Scottish laird from Kinhilt in southwestern Scotland. The estate was temporarily renamed "Kinhilstown" after Adair's lands in Scotland. The original castle of Ballymena was built in the early 17th century, situated to take advantage of an ancient ford at the River Braid. In 1626 Charles I confirmed the grant of the Ballymena Estate to William Adair, giving him the right to hold a market at Ballymena on every Saturday. He hired local Irish as workers on the estate; they served as tenant farmers for much of the next two centuries and more.
In 1641, the local Ballymena garrison were defeated by Irish rebels in the battle of Bundooragh. Ballymena's first market house (on the site of the present town hall) was built in 1684.
In 1690, the Duke of Württemberg, a Williamite general, used Galgorm Castle as his headquarters. Sir Robert Adair raised a Regiment of Foot for King William III and fought at the Battle of the Boyne.
The remains of the 1707 church. The tower was built in 1822 and is a listed building.
By 1704, the population of Ballymena had reached 800. In 1707, the first Protestant (Church of Ireland) parish church was built. In 1740, the original Ballymena Castle burned down. The Gracehill Moravian settlement was founded in 1765. During the 1798 rebellion, Ballymena was occupied from 7 to 9 June by a force of around 10,000 United Irishmen. They stormed the Market House (now the Town Hall), killing three of its defenders.
The first modern Roman Catholic Church in Ballymena was consecrated in 1827. By 1834 the population of Ballymena was about 4,000. In 1848 the Belfast and Ballymena Railway was established. In 1865 Robert Alexander Shafto Adair (late Baron Waveney) started building Ballymena Castle, a magnificent family residence, in the Demesne. The castle was not completed until 1887.
In 1870 The People's Park was established. Now a mature and beautiful setting, it continues to be a very popular park in the early 21st century.
In 1900, Ballymena assumed urban status. Under the provisions of the Irish Land Act of 1903, the Adairs disposed of most of their Ballymena estate to the occupying tenants in 1904. The "old" town hall building, which also contained the post office and estate office, burned down in 1919. Prince Albert, Duke of York (later King George VI) laid the cornerstone to the new town hall on 24 July 1924, and it was officially opened on 20 November 1928.
The Urban District Council petitioned for borough status and the Charter was granted in December 1937. The first meeting of councillors as a borough Council was held on 23 May 1939. The population of Ballymena reached 13,000. Ballymena Castle was demolished in the 1950s. In 1973, the Urban and Rural District Councils were merged to create Ballymena Borough Council. Following local government reoganisation in 2015, the Borough Council was merged with the Boroughs of Carrickfergus Borough Council and Larne Borough Council. During the Second World War, Ballymena was home to a large number of evacuees from Gibraltar. They were housed with local families.
In the 1950s St Patrick's Barracks in Ballymena was the Regimental Training Depot of the Royal Ulster Rifles (83rd & 86th). Many young men who had been conscripted on the United Kingdom mainland, along with others who had volunteered for service in the British Army, embarked upon their period of basic training in the Regimental Depot, prior to being posted to the regular regimental battalions. Many of these young men were to serve in Korea, Cyprus and with the British Army of the Rhine. In 1968 due to a series of government austerity measures, the remaining three Irish regiments, Royal Inniskilling Fusiliers (27th) Royal Ulster Rifles (83rd & 86th) and the Royal Irish Fusiliers (89th) merged to become the Royal Irish Rangers. Early in the 1990s the Royal Irish Regiment, whose Regimental Headquarters was at St Patrick's Barracks, was granted the Freedom of the Borough.
Like other towns in Northern Ireland, Ballymena was affected by the Troubles, a lengthy period of religious and partisan tensions and armed confrontations from the 1960s through 1998. A total of eleven people were killed in or near the town by the IRA and various loyalist groups.
During the later half of the 20th century, Ballymena, like many other once prosperous industrial centres in Northern Ireland, experienced economic change and industrial restructuring; many of its former factories closed. Since the 2010s Ballymena has seen a decline in its retail and manufacturing sectors. Both Michelin and JTI have left the area. Local firm Wrightbus is also struggling citing a downturn in orders. It is hoped that the creation of a manufacturing hub at the former Michelin site will attract businesses to the area.
In March 2000, the actor Liam Neeson, a native of Ballymena, was offered the freedom of the borough by the council, which approved the action by a 12–9 vote. The Democratic Unionist Party objected to the offer and drew attention to his comments from an interview in 1999 with an American political magazine, George. Neeson declined the award, citing tensions, and affirmed he was proud of his connection to the town. Ian Paisley was eventually made a freeman of Ballymena in December 2004 instead.
Ballymena is described by some observers as being at the heart of Northern Ireland's equivalent of the Bible Belt. It has a large Protestant majority. In the early 1990s the Democratic Unionist Party (DUP)-dominated town council banned a performance by the Electric Light Orchestra in the township, saying they would attract "the four Ds Drink, Drugs, Devil and Debauchery". The Council banned the screening of Brokeback Mountain (2005), starring Jake Gyllenhaal and Heath Ledger, as it featured a homosexual relationship. An impersonator of comic Roy 'Chubby' Brown was also banned.
The majority of the town's Catholic population is situated around the Broughshane and Cushendall Road areas. Recently there has been tension in the Dunclug area of the town which now has a Catholic majority. These tensions have been associated with internment bonfires and the flying of republican flags; the town has tried to reduce tensions.
Recreational drugs have been a major problem in the town, earning it the moniker "the drugs capital of the North". However major steps have been taken in recent times to deal with this.
In 2011 it was revealed that Ballymena has the third-highest level of legal gun ownership in Northern Ireland.