In the pic, Johnson could be seen holding her hand up to her face with the ring on full display.
Reps for the couple did not immediately respond to Fox News’ request for comment.
The two were first spotted out and about together in 2017 and have been romantically linked since.
In April, an insider told the outlet that Johnson and Martin, 43, “are very low-key together.”
“They seem to enjoy sharing a quiet life,” they added. “It does seem they are getting more serious.”
Martin was previously married to Gwyneth Paltrow, with whom he shares two children: Apple, 16, and Moses, 14. They were married from 2003-2016.
Paltrow, 48, gave the actress her seal of approval.
“I love her,” the Oscar winner told Harper’s Bazaar. “I can see how it would seem weird because it’s sort of unconventional. But I think, in this case, just having passed through it iteratively, I just adore her. I always start to think of the ampersand sign — what else can you bring in, instead of being resistant to or being made insecure by? There’s so much juice in leaning in to something like that.”
Johnson is considered Hollywood royalty, being the offspring of Don Johnson and Melanie Griffith. At various points in her life, Steven Bauer and Antonio Banderas were her stepfathers, while her grandmother is Tippi Hedren.
The actress and Coldplay frontman collaborated on a music video for the band, which was directed by Johnson.
“That experience was just pretty dreamy. I am so grateful I was given the opportunity,” she told Extra of shooting the “Cry Cry Cry” video. “I was working with such incredible artists in every department. … I felt extremely privileged to make that video.”