The Oak Brook, Ill., producer of private-label food and beverages said in a statement that it would use the proceeds from the sale to pay down debt.
TreeHouse shares were trading up 1.3% at $56.85.
The company expects the unit to post $670 million of sales for 2019. For 2018, TreeHouse reported sales of $5.81 billion.
The division employs more than 800 people and distributes snacks like nuts and trail mix to North America retailers.
The snacks unit operates plants in Robersonville, N.C., El Paso, Texas, and Dothan, Ala. The company in May had said it would close a fourth plant, in Minneapolis, by the end of the third quarter. That plant is not part of the deal, TreeHouse said.
In its first-quarter earnings report, TreeHouse said the "snacks division continues to underperform and [the] plant closure is necessary to position the business for success at lower volume levels."
Subject to customary conditions, the sale to Atlas, the Greenwich, Conn., private-equity firm, should close in the third quarter, TreeHouse said.