"The Newsroom" star - who dated Joel from 2012 until 2014 - has taken to social media to offer her best wishes to the actor, who announced his engagement via Instagram.
Sharing a picture of the proposal, he wrote on the platform, "She said no. Just kiddin..."
The Victoria's Secret model also posted a photograph of the couple kissing, captioning it, "Yours forever (heart emoji)."
And Olivia wasted little time in offering her congratulations to the loved-up couple.
The Hollywood actress - who also dated baseball star Aaron Rodgers between 2014 and 2017 - replied with a series of "100" emojis.
Elsewhere, Wilmer Valderrama, Joel's showbiz pal, also offered his congratulations, writing, "Yes brother!! Felicidades, Here's to an amazing and adventurous life."
Joel Kinnaman and Kelly Gale were first romantically linked in 2019. He was by her side when she landed in hospital to get surgery after a freak horse accident in April and they eventually made their relationship Instagram official in September. By the end of the year, she already introduced him to her family.
When the lockdown was first issued in March, the couple decided to adopt a rescue puppy. "Guess who just became puppy parents?" Kelly proudly introduced her new adorable pet. "We rescued this little cutie yesterday. In the wake of this pandemic a lot of dog shelters are closing and dogs are being killed. Many dogs are in need for temporary or permanent homes. If you are thinking of getting a dog please consider rescuing a doggy in need of a home instead of going to a breeder."