The Memorandum of Understanding between the SLPP and the SLFP will be signed this morning at the Sri Lanka Foundation Institute.
Seniors of both parties, including Opposition Leader Mahinda Rajapaksa and SLFP Senior Vice Chairman Nimal Siripala de Silva, are expected to attend the meeting.
It is not immediately clear whether President Maithripala Sirisena will attend the event.
Political sources said the agreement would also cover the upcoming Parliamentary election where the two parties are expected to contest together.