Gonzalez, who was given the nod over right-hander Tanner Roark, will be opposed by Cubs righty Kyle Hendricks.
The 32-year-old Gonzalez allowed three runs on as many hits in five innings of a no-decision in Game 2 on Saturday. He struck out six and walked two.
Hendricks recorded the win in Game 1 when he permitted just two hits and struck out six over seven scoreless innings. The 27-year-old owns a 2-2 mark in five career starts against the Nationals and is 1-1 with a 1.93 ERA against Washington this season.
The winner of Thursday's game will advance to the NLCS to face the Los Angeles Dodgers.