Becky, who announced her first pregnancy in HELLO! Magazine in December, attended the event with her TV presenter friend Tonia Buxton, instead her husband of three months Harry Needs.
Becky Adlington wowed in a bold floor-length gown
The 25-year-old former Olympic swimmer documented her night at the star-studded awards ceremony on Instagram.
"Amazing night at The Sun Military Awards," she posted alongside a photo of herself with uniform-clad military personnel. "Incredible honour to be in the same room. What they all do is just unbelievable #military #heroes."
Becky, who said that she "couldn't have been more star stuck", uploaded several photos of her fellow famous partygoers.
"I was like a little kid in a sweet shop!" Becky wrote next to a picture of herself with football legend David Beckham, while another photo with Rod Stewart and his wife Penny Lancaster was captioned: "What a moment!!!"
Becky and her friend Toni also took the chance to take a photo with X Factor judge and music mogul Simon Cowell.
"Thank you @toniabuxton for being an amazing date last night!" wrote Becky. "What a lovely man @SimonCowell was!!"
Becky and her husband Harry are set to become parents in June 2015.
"The due date is 4 June so, yes, we must have conceived on the first day of our honeymoon in Venice," Nottingham-born Becky told HELLO!
"But we're not the Beckhams," added Harry. "We won't be calling the baby Venice!"