The 28-year-old actress marked the occasion Thursday by dedicating a sweet message to Butler on Instagram.
"Happy birthday to the love of my lifeeeee," she captioned a photo of herself with the actor.
Hudgens and Butler were first linked in 2011.
The actress opened up about their relationship in an interview with People in May while Butler was filming the TV series "The Shannara Chronicles" in New Zealand.
"Communication is key," she said of making long-distance work.
"I think that if anything's bothering you, don't hold it in," the star added. "Always bring it up and just talk about it. Uncensor yourself and just be open."
Butler previously told Entertainment Tonight he and Hudgens keep their relationship strong by making each other feel important and valued.
"I think you just have to -- it's important to put that other person first," the actor said.
"If you're constantly looking for ways that you can make them happy, and they're constantly looking for ways that they can make you happy, then you kind of lift each other up as much as possible and you can't go wrong," he explained.
Hudgens is known for Disney Channel's "High School Musical" movies, and has since starred on the NBC series "Powerless."
Butler plays Wil Ohmsford on "The Shannara Chronicles," which will move from MTV to Spike for Season 2.
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