The Colombian goalkeeper has been given the nod over Petr Cech, with the duo having been considered 50-50 to start the showpiece match at Wembley.
Per Mertesacker make his first start of the season due to Laurent Koscielny's suspension and Shkodran Mustafi's injury.
Meanwhile, Chelsea manager Antonio Conte picks a starting line-up that will look very familiar to anyone who's watched the Premier League champions this season.
He fields a full-strength side with Diego Costa, Eden Hazard and Pedro starting in a dangerous trident against a weakened Arsenal defence.
John Terry will make his 718th appearance for Chelsea if brought off the bench.
This will be the second FA Cup final contested between Arsenal and Chelsea. The Gunners triumphed in the 2002 FA Cup final in Cardiff 2-0, with goals from Ray Parlour and Freddie Ljungberg.
A win for the Gunners would see them claim their 13th trophy, moving them one ahead of Manchester United on 12.
Wenger, whose future beyond this match remains uncertain, could win his third FA Cup in four seasons by beating Chelsea.
Arsenal XI: Ospina; Mertesacker, Monreal, Holding; Oxlade-Chamberlain, Xhaka, Ramsey, Bellerin; Ozil, Sanchez, Welbeck. Subs: Cech, Coquelin, Elneny, Perez, Iwobi, Walcott, Giroud.
Chelsea XI: Courtois; Azpilicueta, David Luiz, Cahill; Moses, Kante, Matic, Alonso; Pedro, Costa, Hazard. Subs: Begovic, Terry, Zouma, Ake, Batshuayi, Willian, Fabregas.