Some of the best fiction out there is put together with easy to read simple words. Keeping that in mind, you may want to boost your vocabulary a little before starting on the quest of being an author.
You may ask why, if some of the best fiction out there is in simple to understand language. The answer is in your question. The wording tells of a person who does not read much. In order to be a good author (or even a passable one), you need to read. When a person reads they naturally increase their vocabulary. With that being said, their knowledge of word usage increases and they are able to write more complex sentences that have a flow.
Keeping the above in mind, a writer (or author), needs to be able to make their complex thoughts understandable to their audience. When you write fiction, you are not targeting just any reader out there, but people of all walks of life. Today, you may be read by someone who only knows limited English (or the language you wrote in), while the following day an advanced reader.
Knowing this, the other parts of your writing equation need to be filled as well. This means an understanding of grammar and punctuation. Make sure, even if it means a lot of work, to dive into those subjects in order to write the best book you possibly can. If you don’t, there are a lot of people who will learn about it and decide not to read your book.
Most authors, regardless of their abilities, will need to have their work edited. I have my work go through at least 7 critiques before the final product is put through editing looking directly at spelling, grammar, and punctuation to ensure the finished product is the best it can be. You should look at adopting that habit as well if writing is something of a passion for you.
So, your answer is yes, you can write a novel without being a wordsmith, but make sure you cover all the bases (please pardon the cliché) and put out the best novel you possibly can.