BV Investment Partners LP bought a majority stake in RobbinsKersten Direct Inc., or RKD Group, for an undisclosed sum.
In a separate, subsequent release, Brook Venture Partners said its @Brook Fund III fund, which acquired the company in June 2011, was the seller.
Texas-based RKD provides fundraising and marketing services for nonprofit organizations.
The transaction marks the sixth investment of the middle-market buyout firm from its ninth fund.
BV invests in business services and information technology services companies.
The Jordan Edmiston Group Inc. was financial adviser to RKD.