The 34-year-old rose to fame playing the character of Charlotte Hinchcliffe in the British teen comedy.
Emily posted a heartfelt caption alongside a black and white image of her in bed with a baby bump to her 1.9 million followers on Saturday (December 30).
She wrote: “Hello Everyone, it’s been a little while but I’m back with some news. I’m delighted to share with you all that we’re having a baby! I’ve never been so happy and utterly terrified at the same time.
“Please go easy on me. Every day is mixed with thrill, fear, joy, hysteria, topped off with a lot of vomiting – a bit like when you’ve just stepped off of the Oblivion at Alton Towers on a hangover. I’ve got to know my body on such an insane level.
“It’s made me appreciate the one I’ve been given SO much, I’m doing my absolute best to make it a home for the little squid I’m growing.
“We can already sense the baby is reclined on a mattress of peanut butter and jam sandwiches in there, demanding more chocolate buttons. I’m so happy to be writing all of this to you all. You’ve always stuck by me through the years, do stick around to watch me enter my mum era. Christ. Let’s go.”
Her publicist confirmed to PA news agency that she is in a relationship with scientist Alistair Garner.
Emily has also appeared on reality TV shows including ITV’s I’m A Celebrity… Get Me Out of Here! and Dancing on Ice .
The mum-to-be featured in her own sketch show, The Emily Atack Show and was previously a team captain on Celebrity Juice.
Emily is due to star in an upcoming Disney+ adaption of the Jilly Cooper novel, Rivals.
She is the daughter of actress, comedian and singer, Kate Robbins and musician Keith Atack.