The British singer, 28, said "yes" to soccer star boyfriend Andre Gray, 28, on Thursday after he proposed midway through their fourth-anniversary celebrations.
“Guys.. wtf has just happened... He bloody did it, and I said yes," a stunned Pinnock announced shortly afterward on Instagram, alongside a series of romantic pictures capturing the moment.
"I'm marrying my soul mate, the man of my flipping dreams...." she added. "I am lost for words, so I think I'm just going to go cry some more. "@andregray_ I love you so much. My world is literally complete."
The "Shout Out to My Ex" singer has been open about her desire to marry Gray, who plays for Watford Football Club in the English Premier League.
"We both want it so bad," she told Metro.co.uk last month, before adding that they'd so far been unable to take the step because of her hectic recording and touring schedule.
"If I wasn’t in Little Mix we probably would have started planning already," she added. "We’re both really excited so when the time comes, then yeah, we’ll be ready."
On Thursday - ahead of Andre's surprise proposal - she added to this sentiment, posting a romantic image of the couple on a white sand beach alongside the words "Happy Anniversary baby... how has 4 years gone so fast! All I know is I'm another year more crazy about you. I couldn't love you harder if I tried."
Bandmates Perrie Edwards, Jade Thirlwall and Jesy Nelson — who teamed-up with Leigh-Anne when the band was formed by Simon Cowell on The X-Factor — were among the first to congratulate their musical sister.
“My heart is so happy. I absolutely adore you both! YOU. HAVE. A. FIANCÉ," wrote Perrie. "Congratulations to a dream coming true and @andregray_ getting the most amazing girl in the world!”
Jade, added “I love you so muchhhhhh and am so happy for you bothhhhh. I gotta new brother in law y’all.”
Jesy, also wrote “These pictures. Love you both you deserve the world.”
As for Leigh-Anne's new fiancé: he pushed the romantic level even higher, using Spanish to say they would be together "until death."
"Let the caption speak for itself this time...," he posted. "Hasta la muerte."