The 54-year-old actor took to Instagram on Sunday to announce he had popped the question to his girlfriend of nearly two years, Caitlin McHugh, age 31 reported The Daily Mail.
'I asked...she said yes! ...And we lived happily ever after,' he wrote on social media, along with an emoji of a ring.
Caitlin is an actress with previous roles in The Vampire Diaries, Law & Order: Special Victims Unit, and NCIS: Los Angeles.
John and Caitlin have been dating since 2016.
Last year the actor said Caitlin had even won over his Fuller House co-stars.
'They all love her more than me. They're like, "Is Caitlin coming?"', he told Entertainment Tonight.
'She's just a good person,' he gushed of his girlfriend.
The couple have been keeping their relationship low-key, with Caitlin telling People: 'We like to keep our lives private because we've seen what relationships in the public eye can be like and we just like our privacy.
'We don't want the commentary from the masses about what our relationship is or should be. We're very happy together and we hope to be so for a long time.'
Though the couple rarely post about their relationship on Instagram, the actor did share a sweet photo of himself kissing his girlfriend in honour of her birthday earlier this year.
'"Any day spent with you is my favourite day. So, today is my new favourite day." Happy Birthday Babe!' he captioned the photo of themselves wearing onesies.
This engagement means John will be a groom for the second time in his life.
The actor was previously married for seven years to actress Rebecca Romijn, before their divorce in 2005.
John and Rebecca married in 1998, and their divorce was finalised in 2005.