Collateral Promise Law and Legal Definition

Collateral promise refers to a promise to pay the debt of another that is ancillary to an original promise. It is an undertaking which renders the promisor a guarantor or surety upon a debt owing by a third person who is primarily liable. It is not made for the benefit of the party making it. Collateral promise must be in writing to be enforceable. [Dillaby v. Wilcox, 60 Conn. 71 (Conn. 1891)].