Both reality stars confirmed the news Sunday on Instagram.
El Moussa, 38, and Young, 32, both shared a photo of themselves glammed up as El Moussa slipped a ring on the finger of his bride-to-be.
"She said yes!" the HGTV star said. "#FlippingHerLastName."
In the caption of her own post, Young wrote, "The Future Mrs. Tarek El Moussa!!!!"
The two just celebrated their 1-year-of-dating anniversary on Wednesday by posting heartfelt tributes to each other on Instagram and explained how their love story unfolded.
"From the first day I met you, to our first date and our second date when we decided to commit 100% before we barely even knew each other. But we knew what we had was special. We had that butterflies in your tummy, can’t eat, can’t stop smiling soul mate love," Young wrote.
The "Selling Sunset" star revealed that before meeting El Moussa, she had "given up hope" about finding love.
She wrote, "It was unexpected for both of us and it was a moment that changed our lives forever."
Young continued: "You are my very best friend in the whole world. The man I look up to, admire, adore, best daddy, best heart, kind & most important loyal and honest."
Moussa shared two children, Taylor and Brayden, with his ex-wife, Christina Anstead.
In her post, the "Selling Sunset" star hinted at being ready for the lifelong commitment.
"I can't wait to spend the rest of my life with you. Every single day waking up to your sweet face and holding me before bed. I love you beyond anything I could have ever dreamed or imagined," Young concluded. "I promise to love you every single day @therealtarekelmoussa. Happy One Year Anniversary my bunny bear. the love of my life. Me +you."
El Moussa also admitted in his tribute that before meeting Young, he was "a lost and broken man" who didn't think he would find love again.
"July 4th was different," the HGTV star wrote, in reference to their first meeting. "It was the last thing I ever expected but I met the love of my life. The second our eyes connected and we smiled at each other I knew my life would never be the same."
He continued: "She is incredible in every way possible and most importantly she loves and adores Tay and Bray.
"I just love you to the moon and back. You are my everything and you complete me," El Moussa gushed. "I'd be lost without you. HAPPY ONE YEAR ANNIVERSARY MY LOVE!!"
He also addressed public scrutiny regarding their relationship. "Now tell the truth...did you think we were gonna make it?" El Moussa asked.
Fox News' Naledi Ushe contributed to this report