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]
Niccolini has been nominated for seven James Beard Awards, winning three.[7] He has also had parts in several movies, including Inside Man (2006), Arbitrage (2012) and Self/less (2015).[8]