Should he be chosen and make an NFL squad, he would become the first openly gay player in the league.
"I am an openly, proud gay man," he said on ESPN's "Outside the Lines" program.
"I understand how big this is. It's a big deal. No one has done this before. And it's kind of a nervous process, but I know what I want to be ... I want to be a football player in the NFL."
Sam said he told his Missouri teammates of his sexual orientation in August, adding they "rallied around me and supported me."
"We're really happy for Michael that he's made the decision to announce this, and we're proud of him and how he represents Mizzou," Tigers Coach Gary Pinkel said. "We view ourselves as one big family that has a very diverse collection of people from all walks of life, and if you're part of our family, we support you."
"We admire Michael Sam's honesty and courage," NFL Senior Vice President of Communications Greg Aiello said in a statement. "Michael is a football player. Any player with ability and determination can succeed in the NFL. We look forward to welcoming and supporting Michael Sam in 2014."