He participated in expeditions to Greenland in 1898 and 1902, together with the physiologist August Krogh. In 1906, he founded the Arctic Station in Qeqertarsuaq, West Greenland, since 1956 part of the University of Copenhagen. He got support from famous polar researchers like Knud Rasmussen, Mylius-Erichsen and Fridtjof Nansen.
A private person donated the building and running cost were put directly on the Danish state budget.
Morten Porsild managed the station for forty years. In 1946, he returned to Copenhagen, and was succeeded as station head by Paul Gelting.
He was the father of Alf Erling Porsild, Robert Thorbjørn Porsild, Asta Irmelin "Tulle" Egede and Ove Sten Porsild. Apart from botany, Porsild contributed to zoology and ethnography.
He also entered Greenland politics.
(assisted by A Erling Porsild) (1920) The flora of Disko Island and the adjacent coast of West Greenland from 66-71 n. latitude: with remarks on phytogeography, ecology, flowering, fructification and hibernation.