The home of financier Olivier Sarkozy, the former husband of Mary-Kate Olsen and brother of President Nicolas Sarkozy of France, is on the market.

According to the listing with Brown Harris Stevens, Mr. Sarkozy has been renovating this grand 1873 Brooklyn brownstone for seven years. It recently underwent an expansion designed by architect Clive Wilkinson.

The renovations added a glass-walled penthouse with an elevator, roof deck and wrap-around terraces. Mr. Sarkozy also upgraded the kitchen (photos 4 through 12), bathrooms and other finishes to make them "fit for royalty," said listing broker Daniel Neiditch of Brown Harris Stevens Sotheby’s International Realty.

"It’s fresh, it's modern," he said. "It's not dated."

Mr. Neiditch estimated that the value of the renovations exceeds $1 million and is a significant proportion of the $8.25 million price tag on the home when it went on sale in 2009 (it was originally listed for $10 million in 2007).

The master suite takes up the town house's second floor, and offers three en-suite bedrooms with skylights. An elevator connects this level to the ground floor where there is an open living space facing a landscaped garden. The third floor has four more rooms, including a nursery.

The building also has a new garage and backyard. The neighborhood borders the Brooklyn Botanic Garden.

Mr. Sarkozy, who bought this property in 2005 for $5 million, now works as an investment banker at Moelis & Company in New York and spends most of his time there, Mr. Neiditch said. He is trying to sell the town house for use as his pied-à-terre.

The New York Post first reported that Mr. Sarkozy was listing this property in May of last year, but the news resurfaced after a story about him in Women's Wear Daily. "He's not getting any younger and he wants to build an empire away from an office," Mr. Neiditch explained.