The former Sugababes singer took to Twitter to announce her happy news.
She wrote: "Delighted to share the news that my gorgeous @alexpartakis proposed last night!
"Am the happiest girl alive and can't wait to be Mrs HP."
Alex also shared his excitement at being engaged to the 32-year-old, writing: "Am the happiest man in the world today. @Heidi_Range said yes! Can't wait to spend the rest of our lives together xxx [sic]."
Heidi, who was previously engaged to presenter Dave Berry, recently opened up about her new home with Alex.
She told the Mirror: "I have bought an old warehouse in London with alex and we're in the middle of doing it up.
"It's empty so we're starting from scratch. It's a real project but I'm loving every minute. I love getting stuck into the detail. I'm obsessed with light fittings and plug sockets."
Heidi joined the Sugababes in 2001 – replacing founding member Mutya Beuna – and went on to spend 11 years in the band.
They went on hiatus in 2012 and it was confirmed last year that they'd split and had no plans to reunite.
Congratulations to Heidi and Alex on their happy news!