UN spokesman Stephane Dujarric said the German prosecutor would hand over the long-awaited report at Annan’s residence at 5pm (2200 GMT) on Sunday.
He said neither Mehlis nor Annan would make any statement to the media.
Dujarric said earlier that the report would be officially discussed in the UN Security Council on Tuesday, but council members were expected to receive copies of the report on Monday morning “to give them about a day to study it”.
The spokesman said Mehlis, who leaves his post when his commission’s mandate expires on 15 December, was expected to brief the media after his presentation to the Security Council on Tuesday.
He said the search was continuing for a successor to Mehlis should the Security Council decide to approve a Lebanese request for a six-month extension of the UN inquiry panel’s mandate.
Work at home
Mehlis, who took up his post as head of the UN inquiry in June, has emphasised that his employer is the German government and that he has work waiting for him at home.
The UN inquiry is at a crucial stage as investigators this past week wrapped up the questioning of five Syrian intelligence officials in Vienna over al-Hariri slaying.
In his interim report released in October, Mehlis cited “evidence” that senior Syrian and Lebanese security officials were involved in al-Hariri’s murder on 14 February in Beirut.
The Security Council, as a result, unanimously adopted Resolution 1636 on 31 October, demanding that Syria fully cooperate with the investigation and threatening international sanctions if it did not comply.