The Welshman with Team Sky effectively sealed his first Tour de France title by protecting his lead in the time trial on the penultimate stage on Saturday.
Thomas takes an advantage of 1 minute, 51 seconds over Tom Dumoulin into the mostly ceremonial finish on the Champs-Elysees on Sunday.
Dumoulin won the 20th stage by one second ahead of four-time champion Froome, who leapfrogged Primoz Roglic into third place overall.
Thomas finished third in the stage, 14 seconds behind. But that was more than enough with an advantage of more than two minutes at the start of the day.