The 49-year-old actor and the 28-year-old former Miss World America have been linked since 2019.
Duhamel Instagrammed a picture on the beach from when he romantically popped the question. Duhamel revealed that he put a message in a bottle asking her to marry him, and held out the note as Mari beamed behind him. Jan. 8 also marked Mari's 28th birthday.
"It's on!! She found a message in a bottle that washed ashore and said YES!! @audramari," Duhamel captioned the photo.
Duhamel was previously married to singer Fergie, whom he shares 8-year-old son Axl with. They split in 2017 after eight years of marriage, and their divorce was finalized in 2019. He and Mari were first spotted kissing in Toronto in October 2019.
"Josh and Audra met through mutual friends and get along really well," a source told ET at the time. "The two have a great time together and are on the same page about what they want their future to be."
Back in December 2018, Duhamel appeared on Dax Shepard's podcast, Armchair Expert, and said he wanted to date a woman young enough to have kids.
"I'm not 30 years old anymore. I’m 45," he noted at the time. "I want to have more kids in the next few years. So it's more about finding someone young enough to have kids."
"It's not as if I'm out there trying to just f**k anything," he added. "That's really not who I am. I'm trying to find a girl that I can be with, and have a family with."