The model and author confirmed that she is pregnant with the jazz singer's child, after giving birth to their first child Lyra in March.
Her agent confirmed the news of the pregnancy, according to the Daily Mail.
The news arrives a day after the pair attended the Harper's Bazaar event at Claridge's in Mayfair, London.
The granddaughter of author Roald Dahl is due to give birth in April.
Jamie Cullum married Sophie Dahl at the Lime House Hotel in Hampshire in January 2011.
Speaking at last night's ceremony, Cullum told The Sun: "I live an extremely unglamorous lifestyle. I choose to hang out with my friends who aren't in that world and I choose to go to gigs and to the pub and play football.
"To be honest I'm a geek and so is Sophie. We're just two people who met and swiftly fell totally in love. That's the end of the story."