The Sweet Melody singer announced that she and her fiancé, footballer Andre Gray, were expecting on Tuesday afternoon, with a pregnancy photo-shoot posted on her Instagram page.
“We’ve dreamed about this moment for so long and we can’t believe the dream is finally coming true,” the chart-topping star wrote.
Addressing her unborn child, Leigh-Anne added: “We can’t wait to meet you.
Perrie added: “I can’t stop staring at these pictures. You’re a vision. Ily both so much! CONGRATULATIONS my beautiful sister!”
The happy couple also received messages of support on Instagram from Radio 1 presenter Clara Amfo, Stranger Things star Millie Bobby Brown and fellow X Factor winner Alexandra Burke.
Leigh-Anne and Andre have officially been dating since 2016.
The pair announced they were engaged during lockdown last year, after the Watford FC player proposed on their fourth anniversary.
Last week, Little Mix released their first single since the departure of former bandmate Jesy Nelson, a reworked version of their song Confetti, featuring a guest rap from Saweetie.
They also unveiled the song’s music video, which sees them portraying male versions of themselves, and features cameos from Drag Race UK favourites Bimini Bon Boulash, Tayce and A’Whora.
Confetti is the latest song to be taken from their sixth album – also called Confetti – having topped the UK singles chart with their most recent single, Sweet Melody.