Frank Lampard's Derby stunned Leeds to set up a Championship play-off final against Aston Villa after a wild night at Elland Road
The hosts took the lead on the night to go 2-0 up on aggregate when Stuart Dallas tapped in after Liam Cooper's header had hit the post.
Marriott levelled with his first touch before half-time after a horrendous mix-up at the back between Cooper and keeper Kiko Casilla.
Frank Lampard's side turned the tie on its head after the break through Mason Mount and a Harry Wilson penalty, only for Dallas to drift in and fire Leeds back level on aggregate.
Leeds defender Gaetano Berardi was then sent off for a poor challenge on Bradley Johnson before Marriott won it late on with a composed finish.
There was still time for Derby defender Scott Malone to join Berardi in being dismissed after collecting a second booking in time added on.
For Leeds, who finished third in the table, defeat means their spell outside the top flight will stretch to a 16th year.
Derby, meanwhile, become the first team to lose the first leg of a Championship play-off semi-final at home and go on to reach the final meaning Lampard's first season in management will end at Wembley.
What an incredible job he has done. Brilliant.
Terry’s Villa vs. Lampard’s Derby.
The Chelsea boys are competing for their first trophy in coaching