Marcy and his research teams discovered many extrasolar planets, including 70 out of the first 100 known exoplanets[4] and also the first planetary system around a Sun-like star, Upsilon Andromedae.

[7] His collaborators have included R. Paul Butler, Debra Fischer and Steven S. Vogt, Jason Wright, Andrew Howard, Katie Peek, John Johnson, Erik Petigura, Lauren Weiss, Lea Hirsch and the Kepler Science Team.

[1] He graduated with a Bachelor of Arts summa cum laude with a double major in physics and astronomy from the University of California, Los Angeles, in 1976.

Marcy was also one of the project leaders of the Breakthrough Initiatives that will search for intelligent life in the universe, using large radio and optical telescopes.

[15][16] Marcy and his team confirmed Michel Mayor and Didier Queloz's discovery of the first extrasolar planet orbiting a Sun-like star—51 Pegasi b.

[22] In May 2017, Marcy co-authored studies related to laser light emissions from stars, as a way of detecting technology-related signals from an alien civilization.

[31] At least three additional allegations had been made against Marcy as early as 1995 while he was at San Francisco State University, as corroborated by Penny Nixon, then SFSU's sexual harassment officer.

[28] On October 7, 2015, Geoff Marcy posted an "Open Letter to the Astronomy Community" stating "While I do not agree with each complaint that was made, it is clear that my behavior was unwelcomed by some women.

[37] In 2023, a paper co-authored by Marcy with the American Astronomical Society drew criticism from graduate students who had collected data for the project but were not offered co-authorship.