Beginning in the 1960s, Moore played with Phil Lynott and Brian Downey during his teenage years, leading him to memberships of the Irish bands Skid Row and Thin Lizzy, and British band Colosseum II. Moore shared the stage with such blues and rock musicians as B.B. King, Albert King, John Mayall, Jack Bruce, Albert Collins, George Harrison, and Greg Lake, as well as having a solo career.
Moore grew up on Castleview Road opposite Stormont Parliament Buildings, off the Upper Newtownards Road in east Belfast, as one of five children of Bobby, a promoter, and Winnie, a housewife. He left the city as a teenager, because of troubles in his family – his parents parted a year later – just as The Troubles were starting in Northern Ireland.
Moore picked up a battered acoustic guitar at the age of ten. He started performing at a young age, making his live debut in a school band, during the intermission of one of his father's promoted shows. Before getting his first quality guitar (a Fender Telecaster) at the age of 14, and learning to play the right-handed instrument in the standard way, despite being left-handed.
In 1968, after performing with a number of Belfast-based bands, Gary Moore, at the age of 16, was "headhunted" as the replacement guitarist in the Dublin-based band Skid Row and he moved to Dublin. Moore's greatest influence in the early days was English guitarist Peter Green of Fleetwood Mac who was a mentor to Moore when performing in Dublin.
Other early musical influences were artists such as Albert King, Elvis Presley, The Shadows, Buddy Guy and The Beatles. Later, having seen Jimi Hendrix and John Mayall's Bluesbreakers in his home town of Belfast, his own style was developing into a blues-rock sound that would be the dominant form of his career in music.
After joining the group Skid Row with Noel Bridgeman and Brendan "Brush" Shiels, in mid 1968, cutting a number of singles and an album, released in 1970, Skid Row then went on to play shows across Europe and the USA, opening for a number of high profile bands. It was with this group that Gary Moore earned a reputation in the music industry, and his association with Phil Lynott began. Moore left the band in December 1971.
In 1970, Moore moved to England and remained there, apart from two short periods in the United States. In 1973, under the name "The Gary Moore Band", he released his first solo album, Grinding Stone. "Grinding Stone" was issued in North America on Neil Kempfer-Stocker's fledgling record label imprint Cosmos and received "Album of the Year" accolades on KTAC-FM/Seattle-Tacoma, Washington, in 1974.
In 1974 he re-joined Lynott, when he first joined Thin Lizzy after the departure of founding member Eric Bell.
From 1975 to August 1978, he was a member of Colosseum II. With that band, he also collaborated with Andrew Lloyd Webber on the composer's Variations album in 1978.
In 1977, Moore re-joined Thin Lizzy, first as a temporary replacement for Brian Robertson, and on a permanent basis a year later.