Private equity firm New Mountain Capital has turned to Simpson Thacher & Bartlett for counsel on a $1.3 billion deal to recapitalize and take control of AmWINS Group, the largest wholesale insurance broker in the United States.

The deal’s terms call for New Mountain to take over rival buyout firm Parthenon Capital Partners’ majority AmWINS stake, which the latter acquired in 2005. AmWINS employees, who own part of the Charlotte-based company with Parthenon, will continue to hold more than 30 percent of the insurance broker after the recapitalization, according to the agreement.