Antonia Grumbach practiced law at the firm for more than 40 years. She became a partner in 1979 and served as managing partner from 1990-1996. Ms. Grumbach focused her practice in the area of tax-exempt organizations. Ms. Grumbach advised charitable organizations (and charitable trusts) on governance issues, endowment questions, tax issues and public/private partnerships. She handled corporate, tax, and other related work such as licensing, employment, and management agreements for private foundations and publicly supported organizations. Ms. Grumbach facilitated Board retreats and discussions on the fiduciary responsibilities and duties of Boards of non-profit entities.

Ms. Grumbach has been an active member of professional organizations and committees. Ms. Grumbach served two terms as a member of the board of advisors of the NYU program on philanthropy and the law. Ms. Grumbach is Chair Emeritus of Wildlife Conservation Society (having been chair of its board from 2015-2018) and on the board of PILnet, the Global Network for Public Interest. In addition, she served on the board of Teachers College at Columbia University (where she was co-chair of the board for five years), Milton Academy, Mrs. Giles Whiting Foundation (where she was President of the Board for several years), Partnership for Children's Rights, The New Press, Ponagansett Foundation, the William T. Grant Foundation, Henfield Foundation, the NOW Legal Defense and Education Fund, and the Mona Bismarck Foundation. Ms. Grumbach also served as a director of U.S. Trust Corporation and U.S. Trust Company of New York for more than 10 years.

Ms. Grumbach has presented on a wide range of issues including the governance and tax concerns of charitable organizations. She has also contributed to and co-authored numerous publications on fiduciary responsibilities of directors, expenditure responsibility, mergers and consolidations and estate and gift tax issues.