Seal started his business career by selling bottles and corks to Mr. Hudson, one of the most extensive importers of beer in those days. Mr. Hudson traded in cowhides and was the founder and promoter of the first indigo market, which was established under the name of M/s. Moore, Hickey & Co. English merchants hired Seal for his sound judgement on indigo, silk, sugar, rice, saltpeter, and other goods. He was appointed as "Banian" to around twenty first class agency houses out of around fifty or sixty such houses in Calcutta. Later he became a landed property speculator and merchant, successively in partnership with Fergusson Brothers & Co., Oswald Seal & Co. and Tulloh & Co. In these three firms he was said to have lost some thirty Lakh of rupees. He was involved in exporting indigo, silk, sugar, rice, and saltpeter to Europe, and importing iron and cotton-piece goods from England. Seal acquired a number of cargo boats, which were then new to the market, and used old flour mills to ship tons of biscuits to Australia for the first emigrants to its newly discovered gold fields. Later, he put up a mill to refine sugar on the centrifugal principle.