Do you need an agent in order to be a published author? Yes, and no. As with everything in this wonderful profession of writing, there is no hard and fast answer.
For my first book (non-fiction), I did most of the initial submissions on my own to both publishers and agents. At about the same time, an agent took me on and a publisher accepted my manuscript. After the agent and publisher sent me contracts, I still had a friend (an attorney) look them over. After he and I were satisfied with the terms, I signed both.
I eventually severed my relationship with the agent, amicably, and my second contract I negotiated with the publisher directly; again it was non-fiction. I read each clause of the contract, compared it with my first, and was satisfied with the terms. And, I did the same for my third non-fiction book. But, I did have additional wording added to my third contract. You see, now I am also writing fiction.
Most contracts specify the publisher gets first look at your next work. Since my non-fiction publisher does not handle a lot of fiction, I did not want to be in breach of contract by submitting around fiction on my own. So, I spoke up, asked to have the wording in the contract reflect that I was free to submit fiction to other publishers, and the deal was sealed.
Which brings me to: do you need an agent to submit fiction? I do not have an agent. I have not found one that is right for me and what I write. So, I submit to small publishers who specialize in my type of fiction. If I want to submit to "The Big Boys," I would need an agent.
So, for you as the author, you need to determine what it is you want out of your writing career. I am perfectly capable of reading and negotiating a contract on my own, when it comes to non-fiction. And, I have happily signed a contract with a small publisher for my first novel, without the need for an agent. The landscape of publishing is changing every day, with the advent of boutique publishing and epublishing. It is no longer a necessity to have an agent to be a published author.