After education in France and England, Aall settled as a merchant in Porsgunn. From 1810 he was the county clerk in Skien and Porsgrunn, before being appointed to Christian Frederik's government, where he was minister of trade and customs. He was one of the two Norwegian negotiators, alongside Jonas Collett during the Convention of Moss where the Swedish king and the Norwegian government signed a ceasefire agreement following the short war between the two countries. Niels Aall was one of Norway's leading politicians in 1814.