The actress' message came in a celebrity-laden public service announcement for the Give a Damn campaign, a web-based anti-discrimination effort backed by singer Cyndi Lauper's True Colors Fund.
"I'm bisexual," Paquin said, before adding that "one hate crime is committed approximately every hour of every day in this country."
Paquin last year confirmed that she is engaged to her boyfriend and "True Blood" co-star Stephen Moyer.
A representative for the actress could not immediately be reached for comment.
Lauper, Whoopi Goldberg, Elton John and Sharon Osbourne were among the other stars who appeared in the message.
"I've come to realise equality means a lot to people who don't have it and that, as a straight person, I have a responsibility to stand up for gay and transgender people each and every day," Lauper said in a statement.