The 23-year-old pop star and Humes announced that they were expecting the baby in mid-2013 on their respective Twitter pages, reported Daily Mail online.
The news comes just four months after they tied the knot in a lavish ceremony at Blenheim Palace.
In a lengthy statement, the excited mother-to-be wrote "Marvin and I could not be more thrilled to announce that we are expecting our first child mid next year. We have always dreamt of being parents and the news is the best early Christmas present we could have asked for."
While 27-year-old Humes wrote, "Rochelle and I are so excited to tell everyone that we are expecting our first baby! It is absolutely amazing."
Wiseman's pregnancy means she is the second 'Saturday' member to become a mother.
Eldest band member Una Healy and husband Ben Foden welcomed their daughter Aoife in March.