Plait has worked as part of the Hubble Space Telescope team, images and spectra of astronomical objects, as well as engaging in public outreach advocacy for NASA missions.

In 1995, he published observations of a ring of circumstellar material around SN 1987A, which led to further study of explosion mechanisms in core-collapse supernovae.

[7][8] Plait's work with Grady, et al. resulted in the presentation of high-resolution images of isolated stellar objects (including AB Aurigae[9] and HD 163296[10]) from the Hubble Space Telescope, among the first of those recorded.

[13] He went on to perform web-based public outreach for the Fermi Gamma-ray Space Telescope and other NASA-funded missions while at Sonoma State University from 2000 to 2007.

His first book, Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing "Hoax", deals with much the same subject matter as his website.

Plait has contributed to a number of television and cinema productions, either onscreen as host or guest or in an advisory role offscreen.

[21] From 2008 to 2009, Plait served as the president of the James Randi Educational Foundation, which promotes scientific skepticism, a position he eventually stepped down from in order to focus on the "Bad Universe" television project.

[30][31]: 3:10  Five years later, Plait established Badastronomy.com with the goal of clearing up what he perceived to be widespread public misconceptions about astronomy and space science in movies, the news, print, and on the Internet, also providing critical analysis of several pseudoscientific theories related to space and astronomy, such as the "Planet X" cataclysm, Richard Hoagland's theories, and the Moon landing "hoax".

[32] It received a considerable amount of traffic after Plait criticized a Fox Network special accusing NASA of faking the Apollo missions.

[33] Astronomer Michelle Thaller has described Badastronomy.com, as well as Plait's book and essays called Bad Astronomy, as "a monumental service to the space-science community".