The Olympic diver and his husband, 43, shared two separate photographs, in which they are both holding an ultrasound scan - on their personal Instagram pages on Valentine’s Day (14 February) to make the announcement.
Daley captioned his post: “Happy Valentine’s Day!”
And his spouse said: “A very happy Valentine’s Day from ours to yours.”
Neither of the couple confirmed the bay’s gender or revealed any more details about when the baby is expected.
Both posts have already been flooded with messages of congratulations.
The 23-year-old married Black in May 2017 in a fairytale ceremony in front of 120 close friends and relatives at Bovey Castle in Devon.
Tom and Lance first got together in 2013, with the diver coming out publicly in a YouTube video in the months that followed.
In the clip he told fans that his “whole world changed” when he fell in love with a man.