"It was really funny because one of the arguments when the vote went through was that the church came out and said, 'You know, this was a dark day for Ireland,' and all you could see was literally rainbows everywhere, posters of rainbows, T-shirts of rainbows, men and women hugging, men and men hugging, women and women hugging, and yet cut to, 'This is a dark day in the history of [Ireland],'" the Irish actor, 39, told E! News this weekend.
"A dark day in the history of a country is internal civil conflict and war and bloodshed," the father of two added. "It was a great day."
Ireland became the first country to legalize same-sex marriage by a popular vote on May 22. Afterward, the Vatican's secretary of state called the Irish vote a "defeat for humanity."
Farrell, who has a gay brother, has been an outspoken advocate of LGBT rights.
Before the vote, his brother, Eamonn, had to leave Ireland to legally marry his husband, Steven.
"I was a bit concerned about him; he put himself on the line greatly for a cause that he believes in and a message that he wanted to see brought to the point of being a constitutional change," the "True Detective" star told E! about his brother. "I'm sure he will be married [in Ireland] within the next year. He got married in Vancouver seven or eight years ago to his husband, but I think it's time he'll enjoy a home-grown celebration."