"This is essentially a deal on legal assistance on a criminal matter, and when it is finalised later this week it will open the door for the Swedish state prosecutor to question Mr. Assange," Swedish Justice Ministry official Cecilia Riddselius told AFP.
Ecuador had demanded that such an agreement be in place before it would let Swedish prosecutors interview Assange, who has been holed up at Ecuador's embassy in London since 2012.
Swedish prosecutors dropped a sexual assault probe against Assange in mid-August after the five-year statute of limitations expired.
They still want to question him about a rape allegation which carries a 10-year statute of limitations that only expires in 2020.
Assange denies the allegations