According to Greer, he enrolled in Appalachian State University in Boone, North Carolina, but in 1974 he "left traditional college at Boone to enter teacher training at Maharishi International University". As of 2007, Greer was licensed to practice medicine in Virginia and has also been licensed in North Carolina. Greer is former chairman of the Department of Emergency Medicine at Caldwell Memorial Hospital in Lenoir, North Carolina, and a lifetime member of the Alpha Omega Alpha Honor Medical Society.

Greer and his wife Emily have four daughters and reside in the Charlottesville, Virginia area. According to Greer he is a contactee who has coined the term "close encounter of the fifth kind" (a.k.a. CE5) to describe alleged human initiated contact with extraterrestrials. CE5 encounters are "characterized by mutual, bilateral communication rather than unilateral contact." CSETI - The CE-5 Initiative

In 1990 Greer founded the Center for the Study of Extraterrestrial Intelligence, and offers how-to training on initiating contact with extraterrestrial intelligence. Greer also teaches the use of meditation techniques that he claims allow attendees to "remote view" locations and times (past and present), and develop "cosmic consciousness" and supernatural abilities such as precognition. Three years later, Greer founded the Disclosure Project, claiming evidence of extraterrestrial visits to Earth, and a wide-ranging conspiracy. Greer is also the founder of the Advanced Energy Research Organization (AERO) and The Orion Project. Both seek funding for research into perpetual motion and other free energy devices.

The Disclosure Project is an organization started by Greer in 1993 that alleges the existence of a US government cover-up of information relating to unidentified flying objects (UFOs). The Project has adopted Greer's contention that UFOs are spacecraft piloted by intelligent extraterrestrial life, and that the United States government is keeping this secret. Greer also uses the project to disseminate his beliefs that the government has concealed advanced energy technologies obtained from the extraterrestrials by suppressing and hiding them in top secret "black projects" in order not to upset the global geo-political power and energy-sector financial status-quo and its oil industry "special interests".

Greer and the Disclosure Project call for congressional hearings of all data regarding UFOs, including the large amount of information they claim is being hidden, and for release of the technology they claim is being suppressed, particularly free energy sources. He uses written statements and accounts from military personnel and defense industry employees as evidence for the various claims associated with the Disclosure Project.

The Disclosure Project has been well-received by UFO enthusiasts, with speeches from Greer and various other witnesses being presented at various UFO-themed conferences. Greer has held press conferences and embarked on a continuing series of lectures and television appearances trying to raise popular support. Mainstream media coverage of the group mostly centered around a 2001 conference at the National Press Club which was described by an attending BBC reporter as the strangest he had ever seen. Greer convened the conference with more than 100 other contactees offering testimony and arguing for investigations into a UFO conspiracy theory. Such arguments were met with by derision by skeptics and spokespeople for the U. S. Airforce who maintain that there is no convincing evidence for the speculation that UFOs are alien spacecraft.

Greer has appeared on Larry King Live, CBS, BBC, NTV in Japan, Sightings, Encounters, Ancient Aliens on the History Channel, Coast to Coast AM, the Art Bell show, and the Armstrong Williams radio show and hosts an Internet radio segment called "Conversations with Dr. Steven Greer".