Spencer spent almost an hour at CPAC talking to the media and conference attendees. He said he "coined the term" alt-right and was wearing a general admission badge.
Organizers seemed uncomfortable with Spencer's presence on Tuesday morning.
"The 'alt-right' does not have a legitimate voice in the conservative movement," CPAC organizer Matt Schlapp told the Los Angeles Times. He emphasized that no one from the movement was scheduled to speak at CPAC and said he'd "rather (Spencer) not be here."
"Richard Spencer is not on our agenda. We did not invite him," he told the Times. "There's all kinds of people, I suppose, who can buy tickets. We have a constitution. We have laws in this country. And I think it would be better if y'all (journalists) didn't give him attention."
Defiant as he left the conference, Spencer called his ejection "pathetic."
"They threw me out," he said, according to Politico. "I guess they just discovered who I was, because the truth is that people want to talk to me, not to other conservatives."
Thousands of conservatives will descend on the Gaylord National Resort & Convention Center outside Washington D.C. to attend CPAC. The conference runs trhough Saturday.
The Associated Press contributed to this report.