In 1809, at the age of seventeen, he married Nagri Dassee, the daughter of Mohan Chand Dey from the Surtir Bagan neighbourhood of Kolkata.

Seal accompanied his father-in-law on a pilgrimage to northern and western India, and was said to be greatly enlightened by his spiritual experience on the journey.

Seal started his business career by selling bottles and corks to a Mr. Hudson, one of the most extensive importers of beer in those days.

Moore, Hickey & Co. English merchants hired Seal for his sound judgement on indigo, silk, sugar, rice, saltpeter, and other goods.

He was involved in exporting indigo, silk, sugar, rice, and saltpeter to Europe, and importing iron and cotton-piece goods from England.

[3] 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.

From dealings in internal exchanges to contracts for station-building, for the erection of new bazaars, to the revival of transit companies, rare was an undertaking in which he was not an important, though quiet, shareholder.

As a philanthropist, in 1841, Seal founded an alms house at Belgharia (in the suburbs of Calcutta) where 500 people were fed daily on average,[10] and is still open to the poor.

Seal subsequently supplemented this gift by a donation of a lac of rupees for the establishment of a female (lying in) hospital which started functioning in 1838.

[13] In those days, the Hindu community was alarmed, owing to several conversions to Christianity taking place among the boys at missionary schools offering free education.

On Wednesday, 1 March 1842, a gathering of respectable people took place at his house for the formal opening of the Mutty Lall Seal's Free College.

[14] There were eloquent speeches in testimony to his noble generosity and liberal mindset with George Thompson complimenting him as "a Hindu gentleman, who had nobly resolved to consecrate a large portion of the substances he had acquired by honorable exertion, to the intellectual improvement of the youth of his own nation to transmute his money into mind".

The institution was opened free of cost, but only one rupee was charged per month to cover expenses such as books, stationery, and the surplus being expended towards furnishing the school with mathematical instruments.

The institute was initially under the management of the Directors of the parent college of St. F. Xavier, Chowringhee, Calcutta, who furnished teachers to further the cause of secular education.

[17] However, later Seal dissolved the connection between his college and the Jesuits over a dispute that in violation of their pledge, so viands were distributed among the Hindu boys contrary to their religious sentiments.

The college initially started functioning at Seal's house and was later shifted to the present building on Chittaranjan Avenue where it still exists.

Although Seal was a conservative, he was in favor of Roy's efforts of banning sati, supported the cause of women's education as well as remarriage of widows.