Reception
"Conspiracy" aired in broadcast syndication within the United States during the week commencing May 13, 1988. It received Nielsen ratings of 9.4, reflecting the percentage of all households watching the episode during its timeslot. This was a decrease of 0.3 ratings points from the previous episode, "We'll Always Have Paris" and was less than the 10.2 rating received by the following episode, "The Neutral Zone". Due to the nature of the content, a warning was aired before "Conspiracy" was screened in Canada. It was initially banned by the BBC in the United Kingdom, but was later aired on BBC Two in a bowdlerised form. The episode was nominated with "Coming of Age" for Best Makeup at the 40th Primetime Emmy Awards, winning the award, one of three Emmys won by the show that year.
Several reviewers re-watched Star Trek: The Next Generation after the end of the series. Keith DeCandido for Tor.com described the episode as "a nasty episode that doesn't quite cohere into the level of nasty it could" but that the series "doesn't do horror/action all that often, and it serves as a good change of pace if nothing else". He gave "Conspiracy" a score of four out of ten. Zack Handlen of The A.V. Club, thought that while "Conspiracy" was a "hard episode to forget", it was not quite as good as he remembered and did not quite "fit" with the rest of the season. He thought that certain parts of the plot were "idiotic" and the admirals reminded him of a "Bond villain convention". He gave the episode an overall grade of B, writing, "fingers crossed that next time we encounter a danger this sinister, the writers know how to handle it".
Robin Roberts was unimpressed with the episode including elements she considered misogynistic and reminiscent of dated elements of pulp science fiction. She noted that the villainous mother alien is explicitly described as female in the episode, and wrote that it seems to embody female stereotypes of cooperation and an undifferentiated collective self gone too far. Meanwhile, the parasite is opposed largely by human males representing masculine individuality, and her targets and victims too are males. Roberts grants that the episode does give a certain respect to the threat: while it may be evil, the mother alien is also powerful, and thus a legitimate threat to the male-dominated hierarchy of Starfleet admirals depicted in the episode.
"Conspiracy" was included as an honorable mention in a list of the best episodes of Star Trek: The Next Generation by Mike Antonucci of the San Jose Mercury News. It was also included in a list of the best and worst episodes by Scott Thill at Wired magazine as one of the best, describing the reactions to the episode as "polarizing" and suggesting that "Conspiracy" might be worthy of becoming a plot in a future film by J. J. Abrams. Total Film also suggested the episode as a potential plot for the film that would become Star Trek Into Darkness, and described it as "easily one of the greatest episodes of Star Trek: The Next Generation". In 2012, David Brown of Radio Times called "Conspiracy" "a definite high point" in the first season and included it on a list of The Next Generation's greatest moments.
