In order to be a professional librarian, you will have to earn an MLS or MLIS (master’s in library science or master’s in library and information science.) You might want to pursue education as a major/double major becuase some states require that a school librarian also have a teaching certificate or the equivalent. I don’t think there are necessarily any requirements for what your undergraduate degree has to be in so pick a subject you are passionate about.
You might want to check out the information on the websites of the American Library Association or the National Association of School Librarians for more information.
Good luck!