The actress, 52, had previously been married twice and has two children, but said that she’s been gay for most of her life, People reports.
"I tried really hard not to be who I am. I tried super hard," she said. "It was a difficult journey for me to come to terms and be whole and happy with who I am."
The Accused star revealed that she was caught off guard by a journalist's question regarding her sexuality when she made the decision to come clean.
She added: "[A reporter] asked me the question and I thought, 'Hmm, do I say the truth, or do I just say it's none of your business', which is my standard answer.
"I said you know, I'm just going to say the truth.”
McGillis, who co-starred with Tom Cruise in Top Gun, added that she was surprised by the amount of media attention her revelation had received.
"I got on a cruise...I thought the whole thing had just disappeared [after the interview], and then I got a phone call: 'Oh my God, Kelly, you can't believe it, it's everywhere'," she said.
McGillis announced publicly that she "was done with the man thing" last month.