The country star turned 38 on Wednesday.
ET has learned that following the ceremony, at which Lambert was nominated for three awards, the birthday girl's celebrations moved down the street from Bridgestone Arena, to the rooftop of her Casa Rosa bar.
Lambert was joined by her husband, Brendan McLoughlin, as well as famous friends including Jason Aldean and his wife, Brittany, Jon Pardi and his wife, Summer, and Florida Georgia Line's Brian Kelley and his wife, Brittney.
The birthday bash saw Lambert trade out her black Versace CMAs dress for jeans and a white T-shirt, which she wore while enjoying food including a full roasted pig, and while listening to chill country music and '90s pop, including some of Mandy Moore's hits, an eyewitness tells ET.
"Everyone sang 'Happy Birthday' to Miranda. Her husband spoke onstage and embarrassed her in the sweetest way," the eyewitness says. "He spoke about how lucky he is to have her and that everyone in the room means something special to them. Miranda was blushing the entire time!"
The party continued through the early hours of the morning and fans even lined up outside until 4 a.m. to catch stars leaving, per the eyewitness.
Prior to his sweet speech, McLoughlin took to Instagram to pay tribute to his wife on her 38th birthday.
"This world became such a better place with you in it. You are a light for those in the dark, a voice for the ones who can’t be heard and most important of all, you’re the most amazing wife day in and day out," McLoughlin, 30, praised. "I hope today brings you as much joy as you bring to me daily. Happiest of birthdays @mirandalambert. I love you."
Watch the video below for more on Wednesday's CMA Awards.