The 40-year-old journalist, who is currently undergoing chemotherapy, explained that she decided to chop her long locks to take control away from cancer.
"We know in our line of work that appearance is important -- and it's important to anybody and everybody, really -- and I decided I was going to take control of one thing away from the cancer, so I got my hair cut," she said.
Robach was diagnosed with breast cancer last October and has since undergone a double mastectomy and two of eight rounds of chemo.
"Today I'm taking control of something that I have very little control of," Robach explains in a video shot before her salon appointment. "I'm going to cut my hair very short. I've never done this before, but I want to say that I had something to do with how I like, not the cancer."
As her hair is cut in the video, Robach cries and claims the haircut symbolizes a "fresh start, a new chapter."
When GMA's George Stephanopoulos told her her new do looked "fantastic," she thanked him and explained it made her feel free and empowered.