Susan McMartin is an American screenwriter and producer for film and television. She wrote the screenplay of the 2016 film Mr. Church, which is autobiographical. She also co-wrote the screenplay of the 2019 film After. Her television work includes Two and a Half Menand Mom. She also wrote the book Understanding the Fall.

Mr. Church was written from her life experiences. Samuel L. Jackson was initially cast as the family friend and cook who helped raise her. McMartin worked as a writer and producer on the CBS television series Mom and as a writer for Two and a Half Men.