The 22-year-old told his 3.6 million subscribers, as well his followers on Twitter, in a six-minute video called Coming Out.
I'm just going to be really honest," he said. "2014 is truly the year that I have accepted who I am and become happy with that person.
"Today I want to talk to you guys about that and be open and honest, and tell you that I'm gay."
Connor said he'd struggled with his sexuality since he was 12 and at first ignored his feelings.
"Growing up I knew that I was a little bit different than everyone else," he said. "I always just had this feeling that I wasn't the same.
"But it wasn't until I was 12 years old until I really had pinpointed what that was.
"For some reason, my seventh-grade year, I had this thought in the back of my head, 'What if I'm gay?' I immediately was so terrified.
"I'm from a small town in the Midwest. That's not a normal thing there. I didn't know what the word meant. I'd only met a couple of gay people in my entire life.
"It was terrifying to me to have to think that I was something that I knew nothing about, so I immediately pushed it away and tried to not think about it."
But Connor admitted he couldn't ignore what he felt and says he became depressed during his second year at university.
"As anyone who's gone through this knows, you can't not think about it.
"I was up all night for I can't tell you how many nights, just thinking about this. I was scared of it, I never told anyone.
"I tried to avoid it at high school by dating girls. All I wanted to be was like everyone else... but I would feel nothing.
"I felt so isolated... and it wasn't until my sophomore in college until I really thought about it."
He says after telling a friend at university, he then told his friends, parents and siblings.
"They didn't look at me differently, they didn't treat me differently" he said.
"Everyone was so great. They just said, 'OK,' like it was no big deal.
"This whole thing that I had built up inside me to be this huge deal for 22 years, wasn't.
"In just one year I've honestly felt like I am so happy with who I am."
Connor's fans also rallied round the star with hashtags like #weloveyouconnor and #proudofconnor trending in the US.
However, some of his female followers said on Twitter that they were upset that they wouldn't be able to marry him.
Connor Franta joined YouTube in 2010.
His videos include Walking Around Naked, Dirty Habits, Getting Over Someone and 5 Ways To Get Your Crush To Like You Back.
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YouTube star Connor Franta has revealed to his fans that he is gay.