Havertz ran onto Mason Mount's through-ball and skipped by City goalkeeper Ederson Moraes before slotting the ball into an empty net in the 42nd minute for his maiden goal in the competition.
Chelsea added to the first European Cup they won in 2012 to become the 13th multiple winners of the world's biggest club competition.
Manager Thomas Tuchel, who only took over at Stamford Bridge from Frank Lampard in January, got his hands on the trophy a year after losing in the 2020 final with Paris Saint-Germain.
