Evan McMullin officially announced his run as an independent presidential candidate on Monday afternoon.

In a series of tweets accompanying a letter, the former CIA officer and House Republican adviser announced why he is running as an alternative to Donald Trump and Hillary Clinton.

McMullin wrote that working for the CIA and Republicans in Congress has shown him "the numerous areas of government that desperately need reform."

He also lamented the choices for president this year.

"[I] had hoped this year would bring us better nominees who, despite party differences, could offer compelling visions of a better future," he explained in his letter. "Instead, we have been left with two candidates who are fundamentally unfit for the profound responsibilities they seek."

According to McMullin, Clinton is a "corrupt career politician" who "only offers stale economic ideas."

Trump, meanwhile, "appeals to the worst fears of Americans at a time we need unity, not division."

"Given his obvious personal instability, putting him in command of our military and nuclear arsenal would be deeply irresponsible," McMullin said. "We cannot and must not elect him."

Neither Clinton nor Trump represent millions of Americans, McMullin argued.

"With the stakes so high for our nation and at this late stage in the process, I can no longer stand on the sidelines," McMullin concluded. "With that in mind, I have decided to pursue the cause of American renewal and the Presidency of the United States of America."

McMullin, who is 40, signed the letter, "With Hope For Our Future."

Read the full letter on his campaign website.