The boyband member and his childhood sweetheart released a video of them carving the happy news into four pumpkins to the soundtrack of them singing.
"Sometimes the best way to say something is with a pumpkin... and a song," he wrote on his Twitter page. "Me and @mrsgifletcher have some rather exciting news to share with you."
The link led fans to an at home video of the prospective parents carving the words "We're having a baby" into four pumpkins at their kitchen table.
"It's a strain to contain my excitement I can barely get to sleep at night when I know that in a couple of months I'll be holding you in my arms. I'll be right beside you all my life," the pair sang to their unborn child.
Although it is not yet known exactly when their bundle of joy will arrive, the final frame showed an ultrasound with the caption 'Arriving 2014' beneath it.
Congratulations from fans flooded in via Twitter and YouTube and the pair responded warmly to their well-wishers.
Tom's bandmates Danny Jones, Dougie Poynter and Harry Judd were quick to congratulate the duo.
TOWIE's Mario Falcone, who is Giovanna's younger brother, expressed his joy at becoming an uncle for the first time.
"Yay Uncle Mario :)... Congratulations to my sister @MrsGiFletcher and @tommcfly... Cannot wait! So happy!," he tweeted.
Tom and Giovanna started dating at the age of 13 when they studied at the Sylvia Young Theatre School.
See Tom and Giovanna's interview with HELLO! to mark their first wedding anniversary in May.