Marie de Roux was born around 1821 in Lausanne, Switzerland. She moved to England in her late teens and secured employment as a domestic servant in prominent households, including that of Lady Palk at Haldon House, Devon, and later with Lady Blantyre at Stafford House, London. During her time in domestic service, Marie became acquainted with Patrick O'Connor, an Irishman working as a customs officer and moneylender in London. Their relationship evolved into a romantic liaison.

In 1847, Marie married Frederick George Manning, a former railway guard with a dubious reputation, having been discharged under suspicion of involvement in robberies. Despite her marriage, Marie maintained her relationship with O'Connor, who was known for his wealth accrued through moneylending and investments. The complex dynamics between Marie, her husband Frederick, and her lover Patrick set the stage for the tragic events that followed.

On August 9, 1849, Patrick O'Connor was invited to dine with Marie and Frederick Manning at their residence, 3 Miniver Place, Bermondsey, London. During the visit, following a premeditated plan, Patrick was murdered. He was shot at close range in the back of the head and subsequently buried under the flagstones in the Mannings' kitchen. The motive was primarily financial, aiming to acquire O'Connor's wealth.

The day after the murder, Marie visited O'Connor's lodgings, stealing his railway shares and other valuables. Both Marie and Frederick fled separately, each attempting to claim a portion of the stolen assets. Marie was apprehended in Edinburgh while trying to exchange O'Connor's property, and Frederick was captured on the island of Jersey.

Their trial commenced at the Old Bailey on October 25, 1849. Both defendants attempted to shift blame onto each other, but the jury found them both guilty. They were sentenced to death and executed by hanging on November 13, 1849, at Horsemonger Lane Gaol in London. This marked the first joint execution of a husband and wife in England since 1700.