Along with his mother-in-law Vanessa, Liam was joined by Natasha's closest friends at the Roundabout Theatre for the special service.
SJP arrived looking demure in a white jacket, while Uma was elegant in a silk mauve dress.
Natasha died last March following a head injury sustained when she fell during a skiing lesson in Quebec.
She was a big part of the music theatre scene in New York, where she lived with Neeson and their two sons, Micheal and Daniel.
The memorial came just days after Neeson and Vanessa joined friends and family to say goodbye to Vanessa's sister, actress Lynn Redgrave, who recently died of breast cancer.
By Ruth Doherty