A statement on Lord's official website says the Leicester, England-born musician suffered a fatal pulmonary embolism in London after a long battle with pancreatic cancer.
"Jon passed from Darkness to Light," the statement said.
Lord co-wrote some of Deep Purple's most famous tunes, including "Smoke on the Water," and later had a successful solo career following his retirement from the band in 2002. The statement posted on Lord's website said he died "surrounded by his loving family."
Emily Freeman of The Agency Group, which represented Lord for all his live concert work, confirmed the news in an email.
Tributes to Lord flooded Twitter, with artists such as Rage Against the Machine's Tom Morello and Toto's Steve Lukather expressing sadness over his death and praising his musical contributions.
Earlier this month, Lord canceled a performance of his Durham Concerto in Germany. At the time, his website assured fans that it was "not a matter for concern, but it is a continuation of his regular treatment that has just taken longer than anticipated."
Lord had written to fans last year saying he was fighting cancer and would be taking a break from performing "while getting the treatment and cure."
"I shall of course be continuing to write music - in my world it just has to be part of the therapy - and I fully expect to be back in good shape next year," he wrote in August 2011.
Lord got his musical start playing piano, first taking classical music lessons before shifting to rock and roll.
After moving to London to attend drama school, he joined blues band the Artwoods in 1964 and later toured with The Flowerpot Men - known for their hit "Let's Go To San Francisco" - before joining Deep Purple in 1968.
Deep Purple - which featured Lord along with singer Ian Gillan, guitarist Ritchie Blackmore, drummer Ian Paice and bassist Roger Glover - was one of the top hard rock bands of the '70s. Influenced by classical music, blues and jazz, Lord took his Hammond organ and distorted its sound to powerful effect on songs including "Hush," ''Highway Star," ''Lazy" and "Child in Time."
The group went on to sell more than 100 million albums before splitting in 1976.
Lord went on to play with hard rock group Whitesnake in the late 1970s and early 1980s and later, a re-formed Deep Purple.
Associated Press writer Dave Zelio in Chicago contributed to this report.