Publicity for Cruise and his production company will now be handled by Paul Bloch of the PR firm Rogers and Cowan.
The 43-year-old star said Ms DeVette had done “a wonderful job” but would now just represent his charitable work.
DeVette took over Cruise’s publicity in March 2004 after he parted ways with previous representative Pat Kingsley.
The transition coincided with a shift in his public image that saw him speaking at length about his Scientology beliefs and giddily expressing his love for fiancee Katie Holmes.
He also suffered public embarrassment when water was squirted in his face at the London premiere of War of the Worlds in June.
In a statement, Cruise said his sister had “always expressed a desire to oversee and expand the day-to-day activities of my charitable endeavours”.
“This seemed an appropriate time to make that segue and bring Rogers and Cowan on board to handle mine and the company’s entertainment-related publicity needs.”
“I know how important Tom’s charitable goals are to him,” said DeVette in the same statement.
She said she looked forward to raising the profile of her brother’s involvement in children’s health issues, social reforms and “the general betterment of the human condition”.
Bloch’s other clients include John Travolta, Bruce Willis, Sylvester Stallone and David and Victoria Beckham.
“I’m so pleased they brought us on,” he told the Los Angeles Times on Monday.