The former Fab Four member announced on Thursday that he was collaborating with New York City Ballet's ballet master in chief Peter Martins on a new work to be premiered by the company on September 22.
"I am always interested in new directions that I haven't worked in before," McCartney said on his website.
"I became very excited about the idea. When I got back to England after meeting Peter I started writing music and am now in the very final stages of the orchestral score."
He said the composition work differed from writing songs as it was a more abstract exercise in expressing pure emotion "... so you have fear, love, anger, sadness to play with and I found that exciting and challenging."
Martins and McCartney met at the School of American Ballet's Winter Gala in 2010 and began discussing the possibility of working together on a ballet.
"Like the rest of my generation, I grew up being a huge fan of The Beatles so I was thrilled to meet him," said Martins.
"After I got to know him a bit, and knowing of his great love of composing classical music, I asked if he might be interested in doing something for New York City Ballet, and I am ecstatic that he has agreed to write a score for us."
According to the New York Times, the new work is a love story titled "Ocean's Kingdom."
McCartney told the newspaper it was "basically a romantic story" involving two worlds: the ocean kingdom, representing purity, and the earth kingdom, inhabited by "the sort of baddies."
McCartney, 68, is one of the most successful songwriters in pop history, particularly through his affiliation with the Beatles. He has since branched out, and tried his hand at classical music composition with the 1991 "Liverpool Oratorio."
(Reporting by Mike Collett-White, editing by Paul Casciato)
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