Along with Rasmussen, Harald Moltke, and Ludvig Mylius-Erichsen, Brønlund was a member of the 1902-1903 Danish Literary Greenland Expedition.

Here, he studied drawing with Kristian Zahrtmann and taught in Askov at Denmark's largest folk high school.

An expert interpreter, one of Brønlund's responsibilities during the 1906 Danish Expedition to Northeast Greenland under Mylius-Erichsen was to keep a travel diary,[7] and to drive the dogs.

[8] He died in November 1907 of hunger and freezing while travelling back from the Independence Fjord and attempting to return to their base camp.

He was found near the depot in Lambert Land on 13 March 1908 along with his diary that recounted the fate of Mylius-Erichsen and the expedition's cartographer, Niels Peter Høeg Hagen, both of whom died before Brønlund in Nioghalvfjerdsbrae at 79° latitude.