The retired track athlete took to Instagram to tell fans that she and her husband, Andy Hill, had welcomed a daughter on Saturday 23 September.
And they have named her Olivia Ennis-Hill.
The photograph showed the first time Reggie met Olivia, with the caption: “Reggie meeting his beautiful baby sister :) Olivia Ennis-Hill, she was born Saturday night. We are all so in love with her.”
The last time Ennis-Hill shared a photograph of her growing bump was on 1 September when she posted a snap of her doing yoga.
“Just about managing to do a little exercise,” Ennis-Hill wrote in the caption. “Definitely slowing down now. Not long to go.”
The two-time Olympic medalist announced she was pregnant with her second baby in March this year, after retiring from her sporting career in October 2016.
At the time she shared a photo of Reggie holding a book that read: ‘I’m going to be a big brother’ on the cover.
“Someone’s going to be a big brother,” she captioned the shot. “Another little Ennis-Hill on the way. So happy @andyhill18.”
Ennis-Hill married her partner in May 2013 and had her first child in July 2014.