Kate, Britain's Princess of Wales, says she has finished her course of , saying the treatment has given her a new perspective and made her grateful for "simply loving and being loved".
Kate, 42, wife of heir-to-the-throne Prince William, which revealed the presence of cancer and has been undergoing treatment since then.
In a personal message accompanying a video of her with her husband and their three young children, Princes George and Louis and Princess Charlotte, Kate said she would be carrying out a handful of public engagements later this year, but said her path to full recovery would be long.
"As the summer comes to an end, I cannot tell you what a relief it is to have finally completed my chemotherapy treatment," Kate said in her message.
"The last nine months have been incredibly tough for us as a family. Life as you know it can change in an instant and we have had to find a way to navigate the stormy waters and road unknown."
Kate emerged in June at the annual military parade to mark the official birthday of King Charles. In July, she appeared at the Wimbledon tennis championships.
Her office, Kensington Palace, has declined to give any further details about the type of cancer or other specifics about her treatment, other than to say the .
"The cancer journey is complex, scary and unpredictable for everyone, especially those closest to you," she said.
"With humility, it also brings you face to face with your own vulnerabilities in a way you have never considered before, and with that, a new perspective on everything.
"This time has, above all, reminded William and me to reflect and be grateful for the simple yet important things in life, which so many of us often take for granted. Of simply loving and being loved."
In the video, which was filmed in Norfolk, eastern England last month, the princess looked well and healthy.
Princess Kate has only appeared in public twice since her cancer diagnosis, including at Wimbledon. Source: Press Association / Dubreuil Corinne
She and William were grateful for the global messages of support, she said, adding she was looking forward to returning to public duties when she was able, although her program for the remainder of the year will remain light.
"Doing what I can to stay cancer-free is now my focus. Although I have finished chemotherapy, my path to healing and full recovery is long and I must continue to take each day as it comes," Kate said.
"Despite all that has gone before, I enter this new phase of recovery with a renewed sense of hope and appreciation of life ... To all those who are continuing their own cancer journey – I remain with you, side by side, hand in hand. Out of darkness can come light, so let that light shine bright."
