Blues boss Thomas Tuchel made five changes, bringing in Antonio Rudiger, Ngolo Kante, Marcos Alonso, Hakim Ziyech and Timo Werner. Leicester manager Brendan Rodgers made just one alteration, with Jonny Evans coming in for Marc Albrighton.
Chelsea were dominating the early exchanges and Caglar Soyuncu made a hash of the clearance making the early running and a wild swipe at the ball that did not prove costly from Caglar Soyuncu suggests early nerves in the Leicester camp.
In the 16th minute Timothy Castagne got in behind Marcos Alonso down the right and cut the ball back to Jamie Vardy, whose shot was blocked by Reece James.
Four minutes later Youri Tielemans delivered the free-kick Soyuncu's header looped over the crossbar.
The Blues had a big chance on the half-hour mark when Thiago Silva's cross to the back post was taken off the head of Cesar Azpilicueta by Timo Werner with the Spaniard looking primed to hit the back of the net.
Rodgers' side looked a more confident outfit in the second half and were rewarded with the lead shortly after the hour mark through a piece of individual brilliance when Tielemans strode forward and let fly from 25 yaards with the effort flashing past Kepa into the top left corner.
Chilwell headed the ball into the ground which looked destined for the corner but Kasper Schmeichel made a brilliant save, diving to his right to tip it around the post.
Schmeichel then made another world-class save to deny the Blues when he flung himself this time to his left to claw the ball around the upright from Mason Mount's cleanly struck volley.
The Blues had a goal marginally ruled out for offside in the closing stages and in the end the Foxes held on to make it fifth time lucky and secure their maiden FA Cup.
