This type of agreement transfers the obligations of one party under a contract to another party. In real estate transactions, an assumption agreement allows a third party to "assume" or take over the loan of the property's seller.An Assumption Agreement is a legal document through which one party transfers its obligations or duties under a contract to another party. A person who assumes a mortgage takes over a payment from the previous homeowner. This Assignment and. Assumption Agreement may be executed in any number of counterparts. Also called an assignment and assumption. An agreement in which one party transfers its contractual rights and obligations to another party.