The steel tycoon had bought the property on Palace Green in Kensington for 117 million pounds in 2008, when it was declared the most expensive home in Britain.
However, according to the 'Sunday Times', he may end up making a loss on the neo-Georgian building after it went on the market earlier this month for 110 million pounds.
The 12-bedroom palatial home was bought for Mittal's son, Aditya, from Israeli-American financier Noam Gottesman.
The entire first floor of the 14,736 square feet property is dedicated to the master bedroom quarters, with a separate wing referred to as "Mrs Mittal's dressing room".
But Aditya, who is the chief financial officer of the family-owned steel firm ArcelorMittal, and his family reportedly never moved into the new mansion.
While the house does not have a swimming pool, it comes with planning permission for basement work and has a dedicated storage room for art, a flower room, a silver room and tutorial and homework rooms for children.
Lakshmi Mittal himself lives nearby at Kensington Palace Gardens, dubbed as London's "billionaire's row" with neighbours including fellow tycoons such as Roman Abramovich and Len Blavatnik, ranked ahead of Mittal in this year's 'Sunday Times Rich List'.
As a result of the credit crunch and a fall in demand for steel from China, Mittal's fortunes took a hit of an estimated 2.7 billion pounds last year, resulting in him being deposed as the richest man in Britain by Russian industrialist Alisher Usmanov after eight years at the helm of the definitive wealth analysis.
Mittal had paid 57 million pounds for his current home and also owns a 70-million pounds former Philippine embassy in London, intended as a home for his daughter Vanisha.