No, Macmillan does not accept manuscript submissions directly from authors. To submit your manuscript to Macmillan, you will need to go through a literary agent.
However, Pan Macmillan Australia does accept submissions from authors. To find more about their manuscript submission process, take a look at their website.
What other publishers are accepting manuscripts this month?
I understand it is hard to find publishers that accept manuscript submissions! To help authors like you, I’ve put together lists of publishers who are accepting manuscript submissions this month in a variety of genres, including romance, fantasy, mystery, thriller, horror, nonfiction and literary fiction. You can find my full list of publishers on my blog.
Otherwise, check out my pre-querying package or developmental editing services to make sure your manuscript is in top shape before approaching a publisher!