He grew up on the Arctic Station in Qeqertarsuaq, West Greenland, where he acted as assistant to his father.

He authored over 100 scientific articles on the flora of the Canadian Arctic Archipelago and of the Rocky Mountains, as well as numerous popular papers and books, including important flora of Canada's Arctic and northern regions.

He made over 25,000 plant collections (numbers), resulting in over 100,000 specimens which are deposited in the National Herbarium of Canada (CAN) at the Canadian Museum of Nature, Ottawa, and in other herbaria around the world.

Porsild was hired to take part in the Canadian Reindeer Project to bring reindeer-herding to the indigenous populations of northern Canada in the hopes of building a sustainable industry.

Porsild's starwort (Stellaria porsildii), a plant native to mountains in Arizona and New Mexico, is also named in his honor.