Gurley ran for 97 yards and Marshall racked up 66 yards in a game in which the Bulldogs (11-1) prevailed despite being outgained in total yardage by Tech (6-6) 426-379.
Aaron Mitchell completed 14-of-17 passes for 214 yards and two touchdowns.
Georgia faces Alabama next weekend in the SEC championship game and the Yellow Jackets meet Florida State in the ACC title tilt.
Georgia scored 14 points in each of the first three quarters and took a 42-3 lead into the fourth before being shut out the rest of the way.
David Sims ran for 71 yards and scored Tech's only touchdown on a 9-yard run with 7:25 left in the game.
Vad Lee and Tevin Washington combined for 120 yards passing for Georgia Tech. The Yellow Jackets turned the ball over twice.