The couple became engaged on Valentine's Day last year (19) when the "Pirates of the Caribbean" actor asked the singer to marry him during a helicopter ride.
Marking a year since the life-changing gesture, they celebrated by throwing a massive party with some of their closest friends.
"one year ago I said yes to a life of love and evolution... and definitely never a dull moment," Katy wrote on her Instagram, along with a series of snaps from the bash.
Alongside the happy couple, the snaps showed party-goers wearing custom sweatshirts with the initials of the pair, reading "OK".
"We don't do dull doe," Orlando commented below the post.
The event included a large flower wall in the shape of a heart. "Dark Horse" hitmaker Katy wore a pink Prada dress to the event with a heart-shaped belt and heart-shaped earrings, while Orlando was dashing in a black shirt and jacket.
A date for the wedding has yet to be announced.