The Dancing With the Stars winner posted a touching snapshot of herself as a baby, being cradled by her father, Steve, and her mom, Terri.
"Today marks 18 years of life for me, here in Australia and I really don't know where to begin in thanking so many people for an unforgettable journey so far," Bindi captioned the pic. "So I think that I'll start here, with this photograph."
"To be perfectly honest life has changed in a million ways since this photograph was taken," she continued. "Along the way we gained another incredible part of our family, my brother Robert. Our conservation work with Wildlife Warriors took off around the world. Our home, Australia Zoo continued to expand and has become the greatest zoological facility on planet earth. Our Dad, Mum's soulmate and a superhero for us all, passed away."
"However, since this photo was taken, 18 years ago, one life ingredient has remained, unchanged, unbreakable. That is the unconditional love that is shared between my beautiful little family and the loyalty we have to each other and everyone else who has taken this journey with us," Bindi added.
The life-long nature conservationist went on to share that she's "endlessly grateful for the love and light I have been given since Day 1 of my life."
Bindi's father, the "Crocodile Hunter," was killed by a stingray in September 2006 while filming a nature documentary in Queensland, Australia. Bindi was 8 years old at the time of his death, and has spent much of her life working to preserve and honor his memory and legacy.
In a follow-up post, she shared a heartwarming contemporary photo of herself playing in the grass with a baby tiger, and said that, while she doesn't know what life will have in store for her, she will never stop trying to "make a difference in this world with each moment that I'm given."
"Life is constantly evolving and I'm determined to find the light and love around every corner and share this with everyone who is a part of my story," she wrote.
"Thank you so much to every single soul who took the time to read these last two posts, it means so much. I can't wait to see what is yet to come," she concluded.
On Thursday, Bindi chatted with ET about her "crazy and wild" birthday plans, which included playing board games with her "lovely little family" and drinking her first Coca-Cola. She also opened up about how the special day is a "really bittersweet time," in the absence of her dad.