The 39-year-old singer and fashion designer took to Instagram Thursday evening to mark her 10th anniversary as a couple with Johnson, a former NFL football player.
"I fell head over slippers in love with this perfect man 10 YEARS ago today! By chance he knocked on my dreamy cottage door (sigh), I let him in and never let him leave. He is mine, I am his... forever #MAY212010," Simpson captioned the post.
Simpson and Johnson married in July 2014 and have three children, son Ace, 6, and daughters Maxwell, 8, and Birdie, 13 months. Simpson recalled her instant connection with Johnson in an interview with Entertainment Tonight in February, saying she considers the day they met as their anniversary.
"I count the day that we met, because it was pretty instant. It was definitely instant. I think he moved in, like, a month later! So we knew," she said.
Simpson was previously married to Nick Lachey, while Johnson was wed to Keri D'Angelo.
"When you know, you know. Especially both of us," Simpson said. "We knew exactly what we wanted in a person, in a companion, and exactly who we wanted to raise children with. We were that for each other."
Simpson discussed her marriage to Lachey and her childhood experience with sexual abuse in her memoir, Open Book, released in February.