Did HP Lovecraft ever publish a novel?

According to his bibliography on Wikipedia, The Case of Charles Dexter Ward and The Inevitable Conflict¹ are the closest you'll find.

It was first published after his death in the Weird Tales periodical, but has since been republished as a novel.

Here's two of the covers it's had:

¹I can't seem to find much information on The Inevitable Conflict, but it appears to also have been first published in another periodical. One site claims it may not have even been written by Lovecraft.