Fearne Cotton will host the annual event when it returns for its seventh year at The Victoria and Albert Museum in Knightsbridge on October 30.
Lewis - a previous winner at the ceremony - will perform a stripped back show before the event kicks off.
She said: "I am so honoured to be performing at Cosmopolitan's Ultimate Women of the Year Awards. What a privilege to be singing to a room full of such strong, inspirational women."
Alesha Dixon, Professor Green and Katie Piper will be on the judging panel to decide the final winners, alongside Karren Brady and Kristin Hallenga.
Cotton said: "I'm so happy to be hosting Cosmopolitan's Ultimate Women Awards. I've hosted for six years now, and each time we get to celebrate the most incredible women who have shown earth shattering amounts of courage, love, bravery and strength. I'm inspired and humbled year on year."
Alesha Dixon added: "I'm honoured to be judging the Cosmopolitan awards again! Supporting and celebrating women from all walks of life is why I love Cosmo. The night is always so moving and so much fun. I can't wait!"
The awards will also mark Cosmopolitan's 40th anniversary, and will include a special 'ultimate' performer, to be revealed at a later date.
Watch Leona Lewis's interview with Digital Spy below: