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.So I would recommend setting your guarantor approval up first before applying to an apartment. There are many parts to a contract and it would be a co-signing arrangement so all tenant applicants should pass a security check as well. Your guarantor will fill out an application and provide similar documents to a landlord as you, including photo ID and recent bank statements. One is requiring the applicant to have a guarantor or cosigner. These people are liable to pay the rent if the tenant doesn't do so.