After CLIPI, Hummer-Tuttle became a partner and then Chair of the Management Committee and Co-Managing Partner of Manatt, Phelps & Phillips in Los Angeles, where she was affiliated for over 25 years. She has served as the Chair of the Board of Trustees of the J. Paul Getty Trust and as President of The Hummer Tuttle Foundation. Additionally, she has been involved in various civic and philanthropic organizations, such as CalTech, the W.M. Keck Foundation, and the Foundation for Art and Preservation in Embassies.