Gay's role within the Biden Foundation will be focused on ending sexual assault and violence against women, among other causes. As a member of the advisory council, Gay joins a prominent group of leaders, experts and advocates who have been selected to serve as ambassadors for the Biden Foundation.
Gay has been outspoken against domestic violence after losing his mother, Carolyn Hall, to murder by her boyfriend when he was 8 years old.
"William Gay is the real deal -- on and off the field," Biden wrote on Twitter. "He's using his voice to get other men involved to end sexual assault and domestic violence. He understands what this fight is all about. I'm glad to have you on the @BidenFoundation team."
Gay told ESPN website The Undefeated that he was initially skeptical upon receiving a letter from Biden.
"I received a letter, and when I saw 'Joe Biden' on it, I'm like, 'OK, this might be a false letter,' " Gay said. "But then my agent told me about it and then the NFL also told me about, so then I was like, 'OK, it's real.'
"His ideas are similar to what I have going on, what my beliefs are, and trying to end domestic violence. I was glad he thought of me. I jumped at the opportunity -- not as quick as I wanted to, because I got the invite during the season and I'm 100 percent about football. So I tried to focus in on the playoffs, but I was all excited for the opportunity to be invited on the advisory committee."
Gay and Biden were scheduled to speak at the Association of Fraternal Leadership & Values Central 2018 on Friday in Indianapolis.
"What drives me is my mother's story," Gay told The Undefeated. "And this is a way, one, to keep her voice alive; two, just to help someone who is either in their situation or as a child in the same situation, give that encouragement that there are better things out there in the world. As a kid, there's no like, 'Oh, my God, my life is over because I don't have parents.' And for anyone who is in that violent situation or the sexual assault situation, there are people out there who would help.
"I don't think my mom knew people that would help, because this was back in 1992. This is my way of allowing her story to stay alive, her to be alive, and also her story helps someone else."
After his mother was murdered, her boyfriend shot himself. Gay and his three siblings were raised by his grandmother, Corine Hall.
Gay has played 10 of his 11 NFL seasons with the Steelers, save for the 2012 campaign with the Arizona Cardinals. He has recorded 571 tackles, 13 interceptions and 7.0 sacks in 176 career contests since being selected by Pittsburgh in the fifth round of the 2007 NFL Draft.