His research has directly informed policy for threatened species,[6] protected area design, and climate change mitigation in numerous countries.
[13] During his masters and doctoral research years, he founded Beneath The Waves, initially created as a platform for inspiring effective storytelling in the marine science community.
[14][15] In 2014, Gallagher incorporated Beneath the Waves as a non-profit organization in the United States, creating a more expansive mission that included research activities.
[19] Gallagher is a frequent host, wildlife presenter, and talent for Discovery Channel and Shark Week,[20][21] and he has also appeared on Nat Geo Wild.
[23] He is a world authority on sharks,[24][25] conducting research aimed at advancing our understanding of their behavior and physiology, and using this information to create protected areas.
[32][33] In 2018 he began investing heavily in The Bahamas as a research locality, with a project evaluating the benefits of large protected areas for sharks.
[38] The Bahamas work led by Beneath the Waves has generated significant press and has been featured in Forbes, Scientific American, and on Sir Richard Branson's Virgin blog.
Through a unique partnership with tagged tiger sharks, Gallagher and Duarte discovered the world’s largest seagrass meadow in The Bahamas, estimated to be up to 93,000 square kilometers.
From 2021, Gallagher served as the co-Principal Investigator on two multi-year Darwin Plus projects,[49] funded by the government of the United Kingdom, to study the deep-water biodiversity of Bermuda and The Cayman Islands.