© Rex Features
The singer-songwriter will join more than 60 acts previously confirmed for the event, which takes place at London's Roundhouse throughout July.
Other headliners already announced include Scissor Sisters, Ellie Goulding and Faithless.
Nash will perform on July 6, supported by New York indie-folk band Darwin Deez.
Last year's festival saw performances from Oasis, The Saturdays and Kasabian among others.
