Paul McCartney, 68, started dating the 51-year-old New York socialite and businesswoman nearly four years ago following his bitter split from second wife Heather Mills.
McCartney publicist Stuart Bell confirmed recent media speculation over a proposal as true, but declined to give further details on when and how the former Beatle asked Shevell to marry him, saying only "we're all thrilled for him."
The marriage will be McCartney's third; his first wife, Linda, died of cancer in 1998. His 2002 marriage to Mills ended in divorce in 2008.
Shevell was married for more than 20 years to attorney Bruce Blakeman, a close friend of former New York Gov. George Pataki, who appointed her to the board of the Metropolitan Transportation Authority.
She also is the vice president for administration of New England Motor Freight Inc., a New Jersey-based trucking company owned by her father.
McCartney and Shevell were first spotted together in Long Island's Hamptons area in late 2007.
Since then, Shevell has become a red-carpet staple, appearing at the March 23 premiere of "The Boat That Rocked" in London, fashion shows by McCartney's daughter Stella, the Grammys and McCartney's concerts around the world.