Grant Reform and New Transparency Act of 2013 or the GRANT Act - Establishes new standards for awarding federal grants. Requires executive agencies to use merit-based selection procedures in awarding grants and to conduct an evaluation of the ability of a prospective grantee to successfully carry out a grant before awarding it.

Requires the Director of the Office of Management and Budget (OMB) to: (1) upgrade any public website for finding federal grant opportunities so that such website serves as a central point of information for competitive grants, (2) issue and disseminate guidance to aid agencies in establishing merit-based selection procedures for grant programs and in identifying amounts of undisbursed funding remaining in grant accounts, and (3) submit a plan to improve the single audit process for auditing the financial statements and federal awards of a non-federal entity. Sets forth the information required to be included in the public grant website, including grant funds availability and grant award information. Requires agencies to explain to grant applicants the basis for award decisions involving grants exceeding $100,000.