Following Dublin's victory in the 2015 Allianz Football League Division 1 final, O'Carroll held a Yes badge as he was pictured holding the cup on the sideline of the Croke Park pitch alongside Jack McCaffrey.
Making a political statement in the stadium is against GAA rules. The game was played a month before Ireland voted in favour of allowing same-sex marriage.
"I broke the rules, I suppose knowingly," O'Carroll, a five-time All-Ireland winner with Dublin, told the BBC's The GAA Social podcast.
"I suppose in one sense I betrayed the culture of the team, which is you do what you can do for the Dublin jersey, and you don't use the Dublin jersey to promote your interests or agenda.
"I was conscious of that but decided this was a cause worthy of betraying that. Eight years later, I don't regret that. Not that this was some monumental act but it was a fact that I did break the rules.
"I don't regret it, and I'd do it again. It was my agenda in terms of I was promoting a Yes vote, but I'm heterosexual so it wasn't as if I was doing it personally for me. There's rules against lots of things but sometimes there are causes worthy of breaking rules for.
"Just like you see these days with lots of people getting exercised about climate protesters but if you look back in history, in order for something to happen, you have to break rules to create change.
"I really want to highlight how small an act mine was at the time, getting in that picture."
10 days before the referendum, O'Carroll's Dublin teammate Ger Brennan wrote an article explaining why he would be voting No.
"When you're getting in a picture like that, the image you're portraying is that the team is promoting a Yes vote, and it wasn't true to say that everyone on the team agreed with that," said O'Carroll.
"Myself and Ger Brennan were very good friends back then and still are. He's one of the funniest guys you'll meet and one of my favourite people to be around. If I was to meet up for drinks, and I could only pick former Dublin teammates, he'd definitely be one of them.
"He wrote an article against and I wrote one for. Funny enough, we were on a training camp just before the referendum, and we were both injured so we spent the entire weekend together driving around debating it. We had to drive to the gym while they went to the pitch sessions. We were openly chatting about it a lot."
A year before he wrote that article, Brennan had stood in the Hogan Stand as St Vincent's captain following their victory over Castlebar Mitchels in the All-Ireland club final.
He thanked the "girlfriends and boyfriends of the players" for their support that season. Brennan was widely praised for the gesture. O'Carroll said he does not believe Brennan's article a year later detracted from those comments.
Asked why he felt so strongly about supporting a Yes vote, O'Carroll said: "Part of being a social worker is it's not just 9 - 5, part of the training and the ethos is to promote equality, promote rights of others, to advocate for others who don't have a voice.
"It's not that those in the LGBT+ didn't have a voice but for that campaign and referendum, I was happy to be an ally. I've got friends and family members who are gay.
"Football is only a game, and when I'm in it, I'm all in - whatever it takes and all the rest of it. There's a limit to that.
"When I'm on my deathbed, I'm not sure how much I'll think about the matches I've won. I'll think about my family, my relationships, my friendships - those sorts of moments. Obviously, if that's sprinkled with a bit of job from winning some matches, so be it, but I don't think it'll come to mind at the very start."