To maintain his family he started selling bottles and corks in Calcutta initially.He also worked as a clerk in different office. For some days he was a custom inspector of Balikhal. From 1820 to1832 he worked as a middleman for many European commercial establishments.He supplied essential elements to Fort William then the bastion of British Government.After that he began export-import business and earned huge money.He bought 13 trade ships and ammased as much wealth as Rustomjee Cowasjee and Dwarkanath Tagore.He became great merchant princes . About him, Sivanath Sastri wrote,"He never adopted unfair means for earning money. He was well-behaved, polite and helpful to others."
He contributed enough money for the the welfare of common people.He established a guest house at Belgharia near Calcutta and a bathing ghat on the bank of the Hooghly River which is mostly known as Motilal Ghat.He donated the land of Calcutta Medical College. In 1843 Seal's Free College was set up by him and Jews teachers were appointed for spreading the concept of secular education.He also donated huge money and cooperation for the establishment of Hindu Charitable Institution and Hindu Metropolitan College. Motilal Seal also supported Vidyasagar's move for remarriage of widows.
Motilal Seal passed away on 20 May 1854.