Making Hawaii his home from 1857 to 1863, Garrett was initially supported and sponsored by local shell collectors, including the malacologist William Harper Pease.
Running out of funds, Garrett approached the ichthyologist Louis Agassiz, who had moved from his native Switzerland to head the new department of Comparative Zoology at Harvard University.
Within the year he was part of a team that hunted for unusual species all over Polynesia, to sketch and paint them as lifelike as possible and send fishes conserved in alcohol for the growing collection at Harvard.
Completely self-taught, Garrett became a renowned and admired specialist in the field himself: a skilled artist and adventurer-scientist, he eventually found a new sponsor in Johann Cesar (VI) Godeffroy, a wealthy scion of international commerce based in Hamburg, Germany.
Garrett's seminal work Fische der Sundsee was first published in 1872 and remained of primary importance for the next generation of ichthyologists.