The Call the Midwife star - who is pregnant with the couple's second child - proudly displayed her blossoming baby bump in a midnight blue dress, which featured tiered detailing and a thigh-high split.
WATCH: Helen George in Call the Midwife season ten
Soaking up the glitzy atmosphere, Helen, 37, was seen gently cupping her bump as she posed for photos with her partner Jack, who looked equally smart in a coordinating blue shirt and grey tailored trousers.
The ATG Summer Party, in aid of Theatre Artists Fund at Kensington Palace Gardens, was attended by theatre industry figures and supporters who donated generously during the auction, bidding on items including a trip to the set of Sam Mendes' new film Empire of Light starring Olivia Colman and Michael Ward.
Helen George and Jack Ashton at the ATG Summer Party
The couple are due to welcome their second child later this year, with the actress announcing the news on Instagram back in June in a post that showed her standing in a field wearing a floral maxi and smiling as she cradled her growing baby bump. She captioned the sweet image: "Baking number 2. Due in December," and added a baby emoji.
Helen met Jack when filming the BBC series in South Africa in 2016; they now live together with their little girl Wren Ivy in the East End.
The actress is pregnant with her second child
During a previous chat with Daily Mail's You Magazine, the actress - who plays nurse Trixie Franklin - confessed being in the same industry as her beau helped. "It's not like you have time to have hobbies at the weekends," she explained.
"You're on set for a long time every day and you don't get to see many other people. We are like-minded people who understand the industry, the career and the long hours."
Make sure you never miss a story! Sign up to our newsletter to get all of our celebrity, royal and lifestyle news delivered directly to your inbox.