Writing on twitter, Nathan said: ''I can proudly announce that me & the lovely @JessieBaylin are expecting our first child. I'm beyond excited/anxious. Life is beautiful.(sic)''
His spokesman Ken Weinstein added the pair - who married in November 2009 - are ecstatic at the chance to have kids.
He said: ''They are two of the most excited people I know.''
Nathan and Jessie are expecting the baby to arrive in December.
They are the third member of the band to have a child; their cousin Matthew Followill and his wife Johanna Bennett welcomed their son Knox Cameron Patrick Followill in April 2011.
Kings of Leon - known for songs including 'Sex On Fire' and 'Use Somebody' - are currently on a hiatus following their tour of Australia last November, and Nathan has recently been supporting his wife while she toured with her album 'Little Spark'.