No and yes.

To paraphrase Dr. Victoria Harrison from the University of Glasgow in her 2006 paper The Pragmatics of Defining Religion in a Multi-Cultural World, she states that as Theravada Buddhism is atheistic, it would otherwise have to be classified as non-religious. This fact alone puts Atheism in the category of a religion.

The secular academic study of religion is very clear that atheism is a religion, and no matter how many people take umbrage with that notion, it is still objectively a fact. As has been already pointed out in many answers, theism is not required in any way for the formation of a religion. So what is instead used as a definition of religion is a summation characteristics that religions have in common. This is widely accepted not only by (secular) religious scholars, but also by other scientific fields of study such as anthropology. A common framework used is made of seven characteristics of belief. I will include a short blurb illustrating how Atheism fits these characteristics.

1. Narrative - Richard Dawkins himself credits Charles Darwin and evolution with the story of humanities origins
2. Experiential - “Atheism has made me feel free!”
3. Social - There are copious groups and organizations that exist for Atheists to meet and interact with each other, as well as many platforms and mediums from which Atheists to promote atheistic beliefs.
4. Ethical - The vast majority of, if not all atheists adhere to some sort of ethical system. It’s common for Atheists to state that they have morality too.
5. Doctrinal - One of the earliest forms of atheism was secular humanism, and their doctrines and ethics are described in a Humanist Manifesto which most atheists adhere to even if they aren’t familiar with the text.
6. Ritual - This is really the only characteristic which has been tenuous in its connection to Atheism. Although in more modern times, Atheists have began to celebrate the anniversary of Darwin’s birth each February as well as the publication of The Origin of Species each November, and calls for the greater public to celebrate these dates as well.
7. Material - Atheism's connection and beliefs about the material world and material sciences is well documented and common knowledge.

So as illustrated, Atheism does in fact, possess every one of these characteristics. Thus qualifying for all intents and purposes as a religion.