The actor, who has played Detective Elliot Stabler since the NBC crime drama made its debut in 1999, will not be returning for the show's upcoming 13th season, reports TV Line.
Meloni's representative later confirmed to E! News: "It is true - 12 great years and time for the next chapter."
The news comes just a week after NBC boss Bob Greenblatt declared that a deal to bring Meloni back to the series was "nearly done".
Fellow show star Mariska Hargitay will return for season 13, but will scale back her involvement in the drama, having adopted a baby girl with her husband Peter Hermann in April.
Hargitay recently claimed that she is "truly excited" about the upcoming Law & Order: SVU run and the changes it will bring for her character Benson.
The next season of Law & Order: Special Victims Unit will air in the Wednesday night 10pm to 11pm slot on NBC's fall 2011 schedule.