The deal for a 99-year lease will be announced at a news conference, along with details of the revamped stadium featuring retractable seating.
Adapting the stadium is set to cost £150m and the Hammers are expected to move in from August 2016, but the agreement should beforehand allow the venue to be used for the 2015 Rugby World Cup.
Under the agreement, West Ham will be given the right to use the stadium for all their matches under a 99-year deal, giving the club long-term security but ensuring they will have no property interest in the facility.