CASEY GREENFIELD is sitting pretty in her NoHo law office beneath a 1970s poster advertising a heavyweight championship boxing match between Muhammad Ali and Joe Frazier at Madison Square Garden. As a freshly minted specialist in high-stakes family law, which tends to translate as bitterly expensive and occasionally scandalous divorce and custody litigation, she deems the vintage poster an inspiration.

“The first step to engaging quietly and efficiently in a fight is to realize that you’re in one, and that you’re not fighting to be mean or petty, but to recognize your own power,” Ms. Greenfield said hoarsely, as always.

Empowerment is a major theme in Ms. Greenfield’s personal and professional lives, which have neatly dovetailed since she emerged from her own heavyweight and highly public bout of custody litigation — she shares an out-of-wedlock child with the married legal journalist Jeffrey Toobin — to form the boutique firm Greenfield Labby. On Wednesday, it will celebrate its first birthday with a party at the Modern, the Danny Meyer restaurant at the Museum of Modern Art. Nearly 200 people, many in the boldface category, have received invitations. It will not be a typical law firm fete.

But then, Greenfield Labby is not a typical law firm.

The firm, which Ms. Greenfield formed with Scott Labby, 39, a Yale Law School classmate and a former boyfriend, has roughly two dozen well-heeled clients and employs five lawyers, in Manhattan and in Boston. It sees itself as an elite group of “country lawyers” for glittering urban professionals with lots to gain — or lose.