Quang Vinh Thang (Michael) Le, who was originally facing one charge of first-degree murder, entered his plea in B.C. Supreme Court in Vancouver Thursday.
The crown is no longer proceeding with a first degree murder charge against Le.
Six people, including two innocent bystanders, were killed in a gang-related attack in a Surrey, B.C., high-rise in 2007.
Le had been on trial since late September along with Matthew Johnston and Cody Haevischer, who are each charged with conspiracy and six counts of first-degree murder. That case against Johnston and Haevischer is expected to continue. Both have pleaded not guilty.
Two other men charged in the case, Jamie Kyle Bacon and Sophon Sek, will be tried separately at a later date.
Four of the victims, Ryan Bartolomeo,19, brothers Michael Lal, 26, and Cory Lal, 21, and Edward Narong, 22, were described by police as having criminal lifestyles.
A sentencing hearing for Le is scheduled for Dec. 17.