He was born of a family whose ancestors emigrated from Diu to Bombay soon after Bombay came into British possession. His grandfather, Ramdas Manordas, amassed a considerable fortune, which, owing to the premature death of his father, came into the sole possession of Mangaldas at the age of eleven. He had to take charge of the business in early life, though he gave some time to English studies.
On the death of his wife he established a dispensary at Kalyan in her memory and also a special female ward in connexion with the David Sassoon hospital in Poona. As a merchant Mangaldas was upright and successful. In social matters he stood forth as a reformer, and to him the change to election from hereditary succession to the headship of the caste is due.
In 1862 he founded a fellowship in Bombay university to allow graduates to spend some years in Europe. A bequest in his will enabled the university to establish seven similar scholarships. He took keen interest in learning, and in such institutions as the Asiatic and geographical societies. In 1866 he was nominated to the legislative council and sat till 1874.
In 1867 he revived the Bombay association, a political body, over which he presided for a time. In 1872 he was made CSI, and in 1875 the dignity of Knight Bachelor was conferred on him. Besides a large donation to the Indian Famine Fund, Sir Mangaldas is known to have expended 500,000 on charities. He died at Bombay on the 9th of March 1890.