The cause of death has yet to be determined, but Adam Parsons, who manages Thin Lizzy, told BBC News that Moore had died in the early hours of Sunday morning.
The 58-year-old joined Thin Lizzy in the early 1970s after the band's lead singer Phil Lynott brought him into the fold to replace outgoing Lizzy guitarist Eric Bell.
Video: Thin Lizzy, "Out in the Fields"
The Irish native was known for his tumultuous yet steady friendship with Lynott.
During the summer of 1979, Moore left Thin Lizzy in the middle of a U.S. tour. In the mid-1980s, the duo scored a Top 5 English and Irish hit with the single "Out in the Fields" after Thin Lizzy broke up. Lynott died soon after the chart success in January of 1986.
More recently, Moore released a string of solo records over the past decade in the blues-rock vein.
Eric Bell, the Thin Lizzy guitarist Moore replaced, told the BBC today he was "in shock" regarding Moore's death.
"I still can't believe it," he said. "He was so robust."
Moore was fond of Spain and played a guitar festival in Barcelona in 2009 alongside such names as Jackson Browne.