The interview, which also included chats with Jenner's family members, gave an intimate look at the former Olympian's life over the years.
"People look at me differently. They see me as a macho male," Jenner told Sawyer on "20/20." "But my heart and my soul, that female side, is part of me, that's who I am. I was not genetically born that way."
"I hate that terminology 'girl stuck in a guy's body,'" she added. "I'm me, I'm a person, this is who I am. I'm not stuck in anyone's body, it's just who I am."
She also said that she was "never attracted to guys."
Jenner told Sawyer that when she was younger she would try on her mother's and sister's outfits.
"I marked the closet so when I put it back I could put ... everything back in the exact same spot so I wouldn't get caught," she said.
Jenner said that she knew she was a trans woman at a young age and that her first wife, Chrystie Scott, was the first person she confided in.
After Jenner's interview with Sawyer aired on ABC, her former wives spoke out, each expressing support.
Scott said Jenner told her she was a trans woman soon after their 1972 wedding.
"It was such a shock to me," Scott told "Good Morning America," adding: "Understandably, I was speechless. I didn't really know what to say."
She added that despite her shock, she "was really pleased" that Jenner trusted Scott with what Scott called her "deepest, darkest secret."
Linda Thompson wrote a lengthy post about their relationship for HuffPost, documenting their courtship, marriage, the birth of their sons, and their subsequent estrangement.
She also wrote that about three years into their marriage, Jenner told her she was a trans woman. They went to couples' therapy for six months before separating.
"Being married to a woman was not what I had envisioned for my life," Thompson wrote.
She added: "It's impossible for those of us who are comfortable living in our own skin to fully grasp what an imprisonment that must feel like to be born into the wrong body."
Kris Jenner called Jenner a "hero" in a tweet.
Jenner's mother, Esther, said that while it was a "surprise" when she first found out Jenner was transgender, she said she would "always love" Jenner.
People outside Jenner's immediate circle also wanted to show the former Olympic hero their support, and her iconic 1978 Wheaties box started selling for several hundred dollars on resale websites like eBay.
A few months after her Diane Sawyer interview, Jenner, photographed by Annie Leibovitz, appeared on the June cover of Vanity Fair magazine. "Call Me Caitlyn," the cover said.