Conversion therapy aims to change a person's sexual orientation.
"You matter. You belong. And you are loved for who you are," said Rep. Ryan Fecteau, D - Biddeford, the bill's sponsor. "No young person needs to be fixed for something that is not broken."
Maine now joins 16 other states that have already banned the practice, and is the last New England state to do so. Supporters of the ban said conversion therapy has been deemed harmful by every major medical association.
Governor Mills said, "It only attempts to make LGBTQ youth feel ashamed of who they are. As a result they are more likely to experience depression...to struggle with substance abuse."
A bipartisan group of supporters attended Wednesday's signing. The bill got support from every Democrat and ten Republican lawmakers.
But there are some who still take issue with the ban, who said there hasn't been a reported case of conversion therapy in Maine. Opponents also said the part of the law that bans talk therapy goes too far.
"It tells professional people that they can only act in one way...we think that over time the courts are going to get involved," said Michael McClellan, the policy director for the Christian Civic League of Maine. "So many problems - First Amendment rights."
But those who support what is now the law, like some MDI high schoolers who testified about their approval in Augusta, said it ensures rural youth get their voices heard.
"Personally I identify as bisexual," said Colby Bennoch, a sophomore at Mount Desert Island High School. "I don't personally feel that I need protecting," but said he supported this bill, "to help protect those around me from possibly losing their sense of self-worth."