A formal announcement about the extension will be made by the UN secretary general's office later this week.
Last month, the commission had sought an extension on grounds that its work has been affected by the deteriorating law and order situation in Pakistan.
The UN commission had began its work on Jul 1.
It has to submit its report identifying facts and circumstances concerning Bhutto's tragic death on Dec 27, 2007 to UN Secretary General Ban Ki-moon.
The new deadline for the commission to submit its report is by Mar 31, 2010.