| Oldham, Lindsay Joanna | The evolution of dark and luminous structure in massive early-type galaxies | 2017 | University of Cambridge | GMOS-N/NIFS+LGS | UK |
| Onoue, Masafusa | Exploration of the cosmic dawn with high-redshift quasars | 2018 | The Graduate University for Advanced Studies, NAOJ | GNIRS | Other |
| Opitz, Daniela | Imaging and astrometry for the coolest brown dwarfs | 2018 | University of New South Wales | GSAOI+GeMS | Australia |
| Pagnotta, Ashley | Recurrent Novae and Type Ia Supernova Progenitors | 2012 | Louisiana State University | GMOS-S | USA |
| Pajuelo, Myriam | Multitechnique Characterization of Binary Asteroids | 2017 | Institut de Mécanique Céleste et de Calcul des Ephémérides | NIRI+ALTAIR | Other |
| Parker, Alex Harrison | Ultra-wide trans-neptunian binaries: tracers of the outer solar system's history | 2011 | University of Victoria | GMOS-N | Canada |
| Patel, Brandon | Type Ia supernovae: their progenitors and use as cosmological probes | 2015 | Rutgers, the State University of New Jersey | GMOS-N | USA |
| Perley, Daniel Alan | The diverse environments of Gamma-ray bursts | 2011 | University of California, Berkeley | GMOS-N/GMOS-S/NIRI | USA |
| Perrin, Marshall Dimsey | A high angular resolution survey of circumstellar dust around Herbig Ae/Be stars | 2006 | University of California, Berkeley | MICHELLE | USA |
| Pierce, Michael J. | Spectroscopy of extra-galactic globular clusters | 2006 | Swinburne University of Technology | GMOS-N | Australia |
| Pike, Rosemary | On the population of the 5:1 Neptune resonance | 2016 | University of Victoria | GMOS-N | Canada |
| Pomohaci, Robert | A near-infrared view of the evolution, environment and multiplicity of Massive Young Stellar Objects | 2017 | University of Leeds | GNIRS | UK |
| Pope, Erin Alexandra | The role of submillimetre galaxies in galaxy evolution | 2007 | University of British Columbia | GMOS-N | Canada |
| Potter, Daniel E. | A search for debris disks with a dual channel adaptive optics imaging polarimeter | 2003 | University of Hawaii | Hokupaa | USA |
| Pracy, Michael Benjamin | The properties and evolution of galaxy populations in the rich cluster environment | 2006 | The University of New South Wales (Australia) | GMOS-N | Australia |
| Radomski, James Thomas | High-resolution mid-infrared imaging of active galactic nuclei | 2003 | University of Florida | OSCIR | USA |
| Rajan, Abhijith | Exoplanet Meteorology: Characterizing The Atmospheres Of Directly Imaged Sub-Stellar Objects | 2017 | Arizona State University | GPI | USA |
| Randriamanakoto, Zara | Formation of young massive star clusters: a high-resolution multi-wavelength study of intensely star-formation galaxies | 2015 | University of Cape Town, South Africa | NIRI+LGS | Other |
| Rapson, Valerie Ann | Infrared investigations of the composition and structure of nearby protoplanetary disks | 2015 | Rochester Institute of Technology | GPI | USA |
| Rate, Gemma Ann | Galactic Wolf-Rayet stars with Gaia: Origins, Properties and Extragalactic Applications | 2020 | University of Sheffield | GMOS-N | UK |
