Thin Lizzy are an Irish rock band formed in Dublin in 1969. The band initially consisted of bass guitarist, lead vocalist and principal songwriter Phil Lynott, drummer Brian Downey, guitarist Eric Bell and organist Eric Wrixon, although Wrixon left after a few months. Bell left at the end of 1973 and was briefly replaced by Gary Moore, who himself was replaced in mid-1974 by twin lead guitarists: Scott Gorham, who remained with the band until their break-up in 1983, and Brian Robertson, who remained with the band until 1978 when Moore re-joined. Moore left a second time and was replaced by Snowy White in 1980, who was himself replaced by John Sykes in 1982. The line-up was augmented by keyboardist Darren Wharton in 1980.

The singles "Whiskey in the Jar" (1972), "The Boys Are Back in Town" (1976) and "Waiting for an Alibi" (1979) were international hits, and several Thin Lizzy albums reached the top ten in the UK. The band's music reflects a wide range of influences including blues, soul music, psychedelic rock, and traditional Irish folk music, but is generally classified as hard rock or sometimes heavy metal. Lynott led the group throughout their fourteen-year recording career of twelve studio albums, writing or co-writing almost all the band's material. He was the first Black Irishman to achieve commercial success in the field of rock music. Thin Lizzy featured several guitarists throughout their history, with Downey and Lynott as the rhythm section on the drums and bass guitar. As well as being multiracial, the band drew their early members not only from both sides of the Irish border but from both the Catholic and Protestant communities during The Troubles.

After Lynott's death in 1986, various incarnations of the band emerged over the years based initially around guitarists Gorham and Sykes although Sykes left the band in 2009. Gorham later continued with a new line-up which included Downey. In 2012, Gorham and Downey decided against recording new material as Thin Lizzy so a new band, Black Star Riders, was formed to tour and produce new releases. Thin Lizzy have since reunited for occasional concerts.

Rolling Stone magazine describes the band as distinctly hard rock, "far apart from the braying mid-70s metal pack". AllMusic critic John Dougan wrote, "As the band's creative force, Lynott was a more insightful and intelligent writer than many of his ilk, preferring slice-of-life working-class dramas of love and hate influenced by Bob Dylan, Bruce Springsteen and virtually all of the Irish literary tradition."

Two of the founding members of Thin Lizzy, bass guitarist and vocalist Phil Lynott and drummer Brian Downey, met while at school in Dublin in the early 1960s. Lynott, born on 20 August 1949 in West Bromwich, England, to an Irish mother Philomena (1930–2019) and Guyanese father Cecil Parris (1925–2010), was brought up in Dublin from the age of three. Downey was born on 27 January 1951 in Dublin. Lynott joined local band the Black Eagles as vocalist in 1963, and Downey was recruited as drummer in 1965. In 1967, Lynott was asked to join Skid Row by bass guitarist Brush Shiels, who brought teenage Belfast guitarist Gary Moore into the band early in 1968. After a disappointing television appearance in June 1969, Shiels fired Lynott, although they remained on good terms and Shiels subsequently taught Lynott to play bass guitar. Lynott then formed Orphanage with Downey on drums after Downey's previous band, Sugar Shack, had split.

Guitarist Eric Bell, born in Belfast on 3 September 1947, began his career playing in local bands such as the Deltones, Shades of Blue and the Bluebeats, and the last incarnation of Them to feature Van Morrison, between September and October 1966. Bell then moved to Dublin and joined Irish showband the Dreams, but left in 1969 with a view to forming a rock band. An acquaintance of Bell's, Belfast organist Eric Wrixon, also a former member of Them, had also moved to Dublin and joined the showband circuit, but had similar plans to progress towards rock music.

In December 1969, Bell and Wrixon met by chance in a pub in Dublin and found that they shared similar ideas of forming a band, and decided to visit the Countdown Club where they saw Lynott and Downey perform with Orphanage. Lynott was not playing bass guitar at this time, but Bell was particularly impressed by Downey, and introduced himself to Lynott and Downey during a break. When Bell asked if they would consider forming a band together, Downey was initially sceptical, but both men were aware of Bell's musical reputation. They agreed that night on condition that Lynott play bass guitar as well as sing, and that the band would perform some of Lynott's compositions. Bell later said, "From there on in we were a band." Wrixon was also included as organist in the as yet unnamed band, making the initial line-up a quartet. The following week, Lynott visited Bell at his flat and played him recordings of some of his own songs. Bell was impressed: "They were so good. I knew right away I could put my guitar style into them."

The band began to attract attention in the Irish music press almost immediately, as the band began rehearsals in January 1970. On 1 January, New Spotlight magazine announced that Bell and Wrixon were to be a part of a new band. By early February, the press had begun to question the delay in any public announcement of the "Bell-Lynott supergroup". The name Thin Lizzy was announced to the press on 18 February. The name came from an idea by Bell about a robot character in The Dandy called Tin Lizzie, which they adjusted to Thin Lizzy as a playful reference to the local Dublin accent, in which "thin" would be pronounced as "t'in". For some of their early gigs, the band were mistakenly promoted as "Tin Lizzy" or "Tin Lizzie". The group's first gig was at a school hall in Cloghran, near Dublin Airport, in 1970, though sources vary on the date from 16 February, 19 February, and 20 February.