The Missouri defensive end became the first openly gay player to be drafted in league history and seeks to be the first openly gay athlete ever to play in the NFL.
Video of Sam receiving the call from the Rams and coach Jeff Fisher revealed the player's emotion while surrounded by friends, family and his boyfriend.
Sam's emotion carried over into a conference call with the St. Louis media.
"Let me tell you something, if we were playing the Vikings right now, I'd probably have three sacks the first game," Sam said. "Since February and my big announcement, this has been a whole [lot of] speculation of the first openly gay football player, but you know what? It's not about that. It's about playing football.
"Can Michael Sam play football? Yes, I can, and the St. Louis Rams know I can. I am going to give everything I've got to the St. Louis Rams to help the Rams win a championship."
Sam added in a statement: "The moment my name was called was the single greatest moment of my life."
For the Rams, drafting Sam added another significant moment in franchise history that has little to do with sports.
In 1946, a year before Jackie Robinson signed with the Dodgers, the Rams signed Kenny Washington, the first African-American football player in the modern era of the NFL.
That fact was relayed to Fisher not long before the Rams turned in the card with Sam's name. It's a legacy in which Fisher takes pride.
"This is the second historic moment in the history of this franchise," Fisher said. "From that standpoint, from a historic standpoint, I'm honored to be a part of that."
The White House released a statement expressing congratulations from President Obama.
"The President congratulates Michael Sam, the Rams and the NFL for taking an important step forward today in our Nation's journey," the statement, which a White House official emailed to ABC News, read. "From the playing field to the corporate boardroom, LGBT Americans prove everyday that you should be judged by what you do and not who you are."
All along, Sam insisted that he wanted to be known simply as a football player and not as some sort of trailblazer. Now he'll get the chance just a couple of hours down the road from his college home in Columbia, Missouri.
Sam announced that he is gay on ESPN before February's NFL scouting combine. The 6-foot-1, 261-pound Sam earned SEC Defensive Player of the Year honors in 2013 after posting 11.5 sacks and 19 tackles for loss.
At the Senior Bowl in January, Sam worked out at outside linebacker after playing as a defensive end in Missouri's 4-3 scheme. That experiment appeared to hurt Sam's stock to the point where many believed he might not get drafted.
As Friday melted into Saturday and the picks dwindled away, Fisher and general manager Les Snead began considering Sam as a possibility. By the time they were supposed to pick in the seventh round, Sam stood above most players remaining on their draft board.
Two picks before the Rams came on the clock with their two seventh-round compensatory selections, Fisher and Snead had private conversations with chief operating officer Kevin Demoff and owner Stan Kroenke about choosing Sam.
Kroenke, who resides in Columbia and has ties to the University of Missouri, offered his blessing, and Fisher dialed Sam's number.
"I am overwhelmed, I am excited and I'm proud to be a Ram," Sam said. "I knew I was going to get picked somewhere and every team that passed me I was thinking of how I am going to sack their quarterback."
Sam, who fills a role Snead calls "DPR" for designated pass-rusher, joins a crowded group at defensive end that includes Robert Quinn, Chris Long, William Hayes and Eugene Sims.
With that type of talent around him it won't be easy for Sam to make the roster.
"It's going to be very competitive for him, as it will be for some of the other guys with later picks, because of the depth and the talent level at the position," Fisher said.
Fisher also made it clear that Sam will be judged solely on his performance on the field.
Sam's teammates echoed those sentiments.
"Obviously people are going to make something out of it," Long told ESPN.com. "He's not the first gay player to ever play football. He might be the first openly gay professional football player, but there's all types of people from all over in an NFL locker room, it really is a melting pot and it never ceases to amaze me how a locker room can just mesh, people from all different walks of life, so I don't think it's an issue. He's coming to a really good D-line room."
Brooklyn Nets center Jason Collins, who this season became the NBA's first openly gay player, said it is a "great day for the NFL and Michael and his family."
Collins said he also texted Sam in support.
"I sent him a text and hoped he would have gone to my team, the Indianapolis Colts," Collins said. "But I am very happy for Michael that he got drafted and that his dream is coming true and he will have an opportunity to make the team and I wish him luck."
Sam, who said Saturday, "I feel like I'm Clowney" given all the attention he has received since being drafted, saw his followers on Twitter grow by more than 20 percent to 115,500 within two hours of being picked.
However, not everyone was supportive.
Soon after Sam was drafted, second-year Miami Dolphins player Don Jones tweeted "OMG" and "horrible." Those tweets since have been deleted, and Dolphins general manager Dennis Hickey said he plans to "sit down with Don Jones and address [the comments] and handle it appropriately."
Former Texas starting quarterback Case McCoy, meanwhile, tweeted, "ESPN ... You serious right now?" after Sam embraced his boyfriend on national TV after receiving the call from the Rams.
Earlier this week, Sam signed his first endorsement deal, partnering with Visa. Although his marketability is likely to be tied heavily to making a team and playing well, he has received dozens of endorsement deal offers, which is unprecedented for a late-round pick.
Saturday night, an excitable Sam spoke loudly and pointedly about his draft experience, pointing out that he believes he should have been drafted higher after earning so many accolades in 2013.
According to Sam, that will only serve as further motivation.
"In all honesty, from last season alone, I should have been a high, first three rounds [pick]," Sam said. "SEC Defensive Player of the Year, unanimous All-American, I should have gone in the top three rounds easily. But you know what? It is what it is. I'm happy to be a St. Louis Ram. Everything else is history."
In more ways than one.
ESPNNewYork.com's Ohm Youngmisuk, ESPN.com Dolphins reporter James Walker and ESPN.com's Darren Rovell contributed to this report.
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The Rams selected defensive end Michael Sam with the 249th pick in the NFL draft.
Michael Sam's Emotional Reaction
Michael Sam reacts to being drafted by the St. Louis Rams with the 249th pick in the NFL draft.
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Rams coach Jeff Fisher explains the team's mindset of drafting Michael Sam and how they expect he'll help the team win.