Calhoun will lead Blackstone’s private equity portfolio management group, which basically means that he will aid CEOs with various operational challenges. He also will work with Blackstone (BX) during due diligence for new deals, helping to identify post-acquisition business strategies.

“Unlike some other big company CEOs who join private equity firms without really understanding the business, Dave really gets it because he’s been running a company owned by private equity firms,” explains Joe Baratta, Blackstone’s private equity boss. “He understands our firm specifically, but also broader issues of private equity governance, what our intervention strategies are all about and the risks surrounding these deals.”

Calhoun is expected to take a handful of portfolio company board seats for Blackstone, and also will remain as executive chairman at Nielsen.

Fortune has obtained an internal memo Baratta sent to Blackstone employees yesterday. We have reprinted it below:

I am pleased to announce that Dave Calhoun, the former CEO of one of our highly successful portfolio companies, Nielsen, has decided to join Blackstone as head of Portfolio Operations in Private Equity. Dave has had an extensive career as the leader of global scale businesses under both private equity and public ownership. He understands our business, Blackstone’s unique culture, and how to create value in companies. Importantly, Dave has extensive personal experience with our portfolio operations group structure and how we interact with our portfolio companies. In fact, his substantial and positive interaction with our team and his understanding of our firm is what motivated him to choose Blackstone over the myriad other opportunities he had.

In order to continue delivering excellent investment returns to our limited partners and shareholders, we must continuously improve our ability to identify and understand great investment targets, back excellent management teams, and intervene operationally to improve the performance of our companies. Dave makes us better in all of these efforts.

Dave will be splitting his time between working with the CEOs of our existing portfolio companies and working with deal teams to identify new investment opportunities and operational value creation strategies. He also will serve on the firm’s Management and Executive Committees.

I have attached a copy of Blackstone’s public press release regarding this exciting news. Dave will officially start working with us in early January, located on the 44th floor of 345 Park Avenue– please join me in welcoming him to our great firm!

Sign up for Dan Primack’s daily email newsletter on deals and deal-makers: GetTermSheet.com