Thomas H. Lee Partners, a Boston-based private-equity firm, announced Monday that former Viacom Chief Financial Officer Richard Bressler is joining as a managing director and head of the firm’s strategic resource group.

Mr. Bressler will oversee the services that the firm provides to portfolio companies.

Mr. Bressler announced last year that he would leave Viacom to pursue other interests after four years with the media giant. His announcement came as Viacom was preparing to break itself into two separately traded companies, a process that ended late last year.

Before Viacom, Mr. Bressler was chairman and CEO of Time Warner Digital Media and previously played a key role in the controversial merger of Time Warner and America Online.