Biel and Timberlake celebrated 10 years of marriage in October.
"Happy birthday to the person who challenges and inspires me every day," Biel, 40, wrote. She paired the caption with two photos of her and Timberlake aboard a boat.
"The person who keeps me laughing and creating and risking it all," Biel continued. "The person who makes the ordinary extraordinary. You know who you are. I love you 🏻"
Biel and Timberlake celebrated 10 years of marriage in October and revealed they renewed their vows in Italy over the summer.
Biel shared a photo of the ceremony on her Instagram story. "From our vow renewal this summer," wrote Biel, who was smiling and holding up a peace sign with her fingers in the fun snapshot. "In Italy where it all went down."
The location, of course, is of significant importance to Biel and Timberlake, who tied the knot in Italy on Oct. 19, 2012. Since then, the couple has welcomed two children, one in 2015 and another in 2020.
Prior to their anniversary, Biel told ET that she and Timberlake were still very much in love. "Well, I'll have to give Justin the credit in this moment, for this one thing that he always says to me: 'We might be married, but we have to keep dating,' and it's so true," she said. "You just have to keep making time for each other and you have to keep making each other a priority. And do the things that you love together."