Hartley and his seven fellow band members were among the 1,517 people aboard the Titanic who died after it hit an iceberg. According to some accounts, the band played the hymn "Nearer, My God, To Thee" to keep spirits up as the passengers boarded lifeboats in the early hours of April 15, 1912.
The musicians have been hailed as heroes for sacrificing their chances of escape.
"Mr. Hartley and the band were very brave people ... standing by their posts to the bitter end," Aldridge said.
The auction house said the violin has been subject to numerous tests to check its authenticity since it was discovered in 2006. It said earlier this year that the violin was Hartley's "beyond reasonable doubt."
The violin, of German make, was a gift from Hartley's fiancee Maria Robinson, and was engraved with the words "For Wallace on the occasion of our engagement from Maria." It can no longer be played, Aldridge said.
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Sylvia Hui can be reached at http://Twitter.com/sylviahui