A guarantor agreement is an agreement of a third party to provide assurance of payment in the event the party involved in the transaction defaults. This Guaranty is irrevocable and part of the Lease Contract and shall be performed in the county where the dwelling unit is located.A guarantor is a person who will cosign an apartment lease alongside a tenant, guaranteeing to pay the rent if the tenant fails to do so. A lease guarantor form is an agreement that makes a guarantor responsible for a tenant's actions.