A guarantor is a person or a company who will co-sign on your lease in case you do not qualify to rent an apartment in New York on your own. A guarantor guarantees the lease in case the tenant doesn't qualify on their own for a New York City apartment.In most cases, guarantors will fill out the same application as a full lessee. The difference being that some landlords require only a credit screening. Private landlords may be tougher, and may refuse to allow you to rent if anyone in the apartment has bad credit, or they may not care. A guarantor is someone who cosigns the lease agreement. They are responsible for any rent payments that you cannot or do not make. A company securing housing for its employee can also act as a guarantor. The guarantor is usually a parent, family member, or close friend who is willing to be legally responsible for the rental apartment. Only those 18 years or older, who will reside in the property, may fill out an application.