'Fireflies' follows 'Trouble' and is the second single from the standard edition of the album.
"Hi everyone I have a really important announcement to make," Lewis said.
"I'm about to tell you the next single from Glassheart is going to be fire... 'Fireflies'."
She added: "This song is really special to me, really important and has such a meaningful and powerful message behind it.
"I think in the run-up to Christmas it's going to be a really powerful song. I'm just really excited about it."
"I've got some really great performances coming up I'm going to be singing it on, I can't wait for you guys to see it. I can't wait for you guys to see the tour, it's going to be really special."
Lewis was recently criticised by singer-songwriter Jake Bugg, whose self-titled debut album went in to the charts at number one over the weekend.
Watch Leona Lewis talking to Digital Spy about Glassheart below.