Niccolini joined the Four Seasons Restaurant in 1977 and quickly became its public face.[3][4] In 1994, he and Alex von Bidder became its primary operating partners.[4] Niccolini created a club-like dining room at the restaurant named the "Grill Room", where patrons conducted business during lunch, although he remarked that "everybody [in the room] claims to be serious, but they are actually having fun."[5][6] Niccolini was forced to resign from the Four Seasons Restaurant in December 2018 over accusations of sexual misconduct.[4]
In June 2015, Niccolini was charged with the sexual abuse of a 28-year-old woman at the Four Seasons Restaurant.[10] In March 2016, he pleaded guilty to misdemeanor assault, admitting that he had "put his hands on the woman, causing scratches and bruises to her hip and thigh".[11]