One of the founding fathers of progressive rock, the British musician is known for songs including In The Court Of The Crimson King and I Believe in Father Christmas.
He died on Tuesday after “a long and stubborn battle with cancer”, said his manager.
The news comes nine months after Lake’s band-mate Keith Emerson died.
Keyboardist Emerson died of a self-inflicted gunshot wound, coroners in the US said.
Lake’s manager Stewart Young wrote on Facebook: “Yesterday, December 7th, I lost my best friend to a long and stubborn battle with cancer.
“Greg Lake will stay in my heart forever, as he has always been.”
‘Greatest music made for love’
Born in Bournemouth, Lake was given his first guitar at the age of 12 and took lessons from a local tutor called Don Strike.
He formed a close friendship with fellow student Robert Fripp, with whom he formed King Crimson in 1969.
Their debut album In The Court Of The Crimson King, featuring songs including 21st Century Schizoid Man, set a standard for progressive rock and received a glowing, well-publicised testimonial from The Who’s Pete Townshend.
But their success was short-lived. Within a year, founding member Mike Giles quit and Lake refused to work with the band – although he stayed around long enough to sing on their critically-reviled second album, In The Wake Of Poseidon.
Image caption Lake (right) with Carl Palmer in 1971 as ELP were recording their album Trilogy
The singer and bassist was then approached by Emerson, who had supported King Crimson on a North American tour – and needed a singer for his new band.
Joined by Atomic Rooster drummer Carl Palmer, ELP made their live debut at the Guildhall, Plymouth, in 1970 – before a career-making performance at the Isle Of Wight Festival.
Unusually, the band combined heavy rock riffs with a classical influence, and scored hit albums with Pictures at an Exhibition, Trilogy, and Brain Salad Surgery – many of them produced by Lake himself.
Tarkus, released in 1971, featured an opening track lasting more than 20 minutes, inspired by the fictional Tarkus character – a half-tank, half-armadillo creature that would appear on stage at gigs.
Their ambitious light shows and on-stage theatrics were the epitome of 70s rock excess, and several punk acts cited ELP as one of the bands they were reacting against.
But the band sold more than 48 million records, and Lake continued to be an influential and popular touring musician even after the band wound down in the late 1970s.
“The greatest music is made for love, not for money,” Lake is quoted as saying on his official website.
“The early ELP albums were pioneering because there is no standing still; time is always moving forward.”