Bratton is expected to leave office at the end of October, the Los Angeles Times reported. He will become chief executive of Altegrity Security Consulting, a new company designed to help governments develop police departments.
"There is never a good time to leave, but there is a right time," Bratton said at a news conference. "It is the right time."
The announcement came as a surprise to Mayor Antonio Villaraigosa and other city officials, the newspaper said.
"With Chief Bratton at the helm, the Los Angeles Police Department transformed itself into a beacon of progress and professionalism, a department seen as a partner, not an adversary, no longer bound by the misdeeds of the past," Villaraigosa said at the news conference.
"Bratton has done an amazing job of turning around this department in the aftermath of a tortured history and really created a new department for the 21st century," said John Mack, who heads the civilian Police Commission, which oversees the LAPD.