In the field of conservation management he has, among other work, reviewed the extinction risk of all Australian birds every decade since 1990, each time producing action plans that have helped set the national agenda. His work with Indigenous Peoples is built on his leadership of a team that created the first global map of Indigenous Peoples lands.
In the field of taxonomy, he has made substantial contributions to the development of guidelines for transparent and collaborative governance of taxonomic lists, with the aim of ensuring that global taxonomic lists have the highest levels of reliability and accuracy and so are more likely to be adopted by users of taxonomic lists worldwide.
He also works at a regional level on various aspects of sustainability including renewable energy and thermal comfort. Professor Garnett has been honoured with several prestigious awards, including a Serventy medal by BirdLife Australia, of which he has been elected as a Fellow, and a Whitley Gold award in recognition of his outstanding contributions to science publication. He has also been appointed by parties to the Convention on Migratory Species as a co-counsellor for birds.