The couple, who also have 18-month-old son Logan, shared the news on social media on Friday, with Team GB rower Glover asking for advice on how to look after three children under the age of three.
Glover, 33, posted a picture of the feet of both of their newborns next to their older son’s on Instagram to reveal the news.
She wrote: “We’re gonna need a bigger boat!
“Welcome to the world little ones. Your big brother is already setting the pace and is so pleased to meet you.”
She added: “Tips for surviving 3 under 2 on a postcard please.”
Wildlife presenter Backshall, 46, posted a picture of the babies’ hands.
He wrote: “Being a twin is like being born with a soulmate.
“A best friend always on hand to play, fight, argue and make up stories with. And Helen should know, being a twin herself.
“All I know is that life is about to get double the crazy. And we couldn’t be happier. @helenglovergb.”
Glover, who along with her rowing partner Heather Stanning won Team GB’s first gold medal at the London Olympics in 2012, announced she was expecting twins in March 2018 but lost one of the babies a month later while pregnant.
She went on to give birth to Logan in July 2018.
Glover and Deadly 60 host Backshall, who recently received an MBE for services to charity and wildlife conservation, married in September 2016 after dating for around two years.