Lewis, who won the British television talent show "The X Factor" and has topped charts around the world, was signing copies of her autobiography at a store in Piccadilly Circus on Wednesday when she was punched in the head.
Under the act, people who may have a psychiatric disorder can be held against their will and given treatment.
He will appear at City of Westminster Magistrates' Court on October 26.
"My brother saw the whole incident," one fan at the book store told the BBC after the assault. "He (the attacker) walked up there with the book, she signed it and, as she looked up, he just punched her."
Lewis, whose debut album entered the U.S. charts at number one in 2008 -- the first British woman to achieve the feat -- was badly shaken but did not need hospital treatment.
(Reporting by Stefano Ambrogi; Editing by Andrew Dobbie)
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