Borders Group Inc. is in the final stages of preparing a bankruptcy filing, clinching a long fall for a company with humble beginnings that helped change the way Americans buy books but failed to keep pace with the digital transformation rocking every corner of the media landscape.

The troubled Ann Arbor, Mich., bookseller could file for Chapter 11 bankruptcy-protection as soon as Monday or Tuesday, paving the way for hundreds of store closings and thousands of job losses, said people familiar with...