The 2019 ATP Finals (also known as the 2019 Nitto ATP Finals for sponsorship reasons) was a men's tennis tournament played at the O2 Arena on indoor hard courts in London, United Kingdom, from 10 to 17 November 2019. It was the season-ending event for the highest-ranked singles players and doubles teams on the 2019 ATP Tour and was the 50th edition of the tournament (45th in doubles). The singles event was won by Stefanos Tsitsipas over Dominic Thiem in three sets. In doubles, Pierre-Hugues Herbert and Nicolas Mahut defeated Raven Klaasen and Michael Venus in straight sets.

Stefanos Tsitsipas is a Greek professional tennis player. He has been ranked as high as world No. 3 by the Association of Tennis Professionals (ATP), which he first achieved on 9 August 2021, making him the highest-ranked Greek player in history alongside Maria Sakkari.