Private equity firm Kohlberg & Co will spend $438 million for the 160-year old business. Steinway Musical Instruments also produces Bach Stradivarius trumpets, Selmer Paris saxophones, and CG Conn French horns, and holds more than 127 patents for musical instruments.
Kohlberg will pay $35 per share, 15 percent more than the stock's closing price on Friday of $30.43.
"Our agreement with Kohlberg represents an exceptional valuation for our shareholders," said Michael Sweeney, chairman and interim chief executive.
Shares in Steinway have risen more than 70 percent this year.
Kohlberg partner Christopher Anderson said the firm was looking to help Steinway expand globally, "while ensuring the artisanal manufacturing processes that make the company's products unique are preserved, celebrated and treasured.”