The property, known as Old Mill Farm, had been on the market since 2007, when it was listed for $39.5 million. It had recently been advertised for $29.7 million.
The Greenwich Time reports that, according to town property records, the estate was bought by Cosette Property LLC.
It includes a 16,000-square-foot Tudor-style mansion that was built in 1926 for financier George Lewis Ohstrom. It also has a five-horse stable, log cabin, 60-foot swimming pool and a stream-fed pond.
The house languished on the market for three years, and Gibson repeatedly slashed the asking price - most recently knocking $10 million off the price tag.
The Bravehart star bought the property for $9.3 million in 1994, when he was married to his wife Robyn. The 59-year-old actor recently split from girlfriend Oksana Grigorieva, with whom he has a 7-month-old daughter, Lucia. He began dating the 39-year-old Russian musician last year.