Guldberg worked at the Royal Frederick University. Together with his brother-in-law, Peter Waage, he proposed the law of mass action. This law attracted little attention until, in 1877, Jacobus Henricus van 't Hoff arrived at a similar relationship and experimentally demonstrated its validity.

In 1890, he published what is now known as the Guldberg rule, which states that the normal boiling point of a liquid is two-thirds of the critical temperature when measured on the absolute scale.

From 1866 to 1868, 1869 to 1872 and 1874 to 1875 he was the chairman of the Norwegian Polytechnic Society.